Class variants

During the creation process of WoW, one central priority of the dev team obviously was the recognition value of the game for those who had played the RTS series, especially Warcraft 3. While some classes were pretty clear-cut (the only RTS counterpart of WoW's Paladin class was the Paladin hero unit), others were more diverse (the Mage class combines elements of the Archmage, the Sorceress and the Lich; while the Warrior combines elements of the Mountain King, the Blademaster and the Tauren Chieftain; the Druid is a mix of the Druid of the Fang/Talon and the Keeper of the Grove etc). The Shaman definitely took the cake in that regard (a synthesis of the Shadow Hunter, Farseer and Tauren Chieftain hero units as well as the Spirit Walker, Witch Doctor and Shaman unit), and it shows.

This attempt to provide all factions with their own fanservice turned out to be a problem right from the start, as it was impossible to balance the two classes that were supposed to be typical for their respective factions (Shamans and Paladins); and for balance's sake both classes were made available for each faction (albeit with very wobbly justifications). Later on, this issue became relevant again when the existing classes were opened up to yet more races under equally flimsy pretenses.

Class variants are intended to be a solution to this problem - they're supposed to expand on the class roster by

(a) generally introducing additional classes that are varieties of the existing baseline classes and

(b) bringing the existing classes more in line with their racial character and lore where it's feasible.

Technically and from any game mechanic perspective however, in either case they're functionally identical with their base classes. The idea is NOT to add new classes and, as a consequence, open a new can of worms when it comes to balancing and patching - the changes are merely cosmetic and literally nothing else (i.e. not even like having one race-specific spell as it was the case in Vanilla). The most common change would be one of class names and occasional skill denominators and visual effects; in some cases however the class also changes the basic magic types (frost, fire, shadow, arcane, nature, holy) on which the class relies.

Generally, this change would open several ways the character class system could be modified:

• Additional options: the most baseline (and probably least controversial) change would be the addition of new class variants that exist alongside the base template. The most basic example would be the Necromancer to the Warlock template.
• Race-specific replacement: some races would get replacement class variants that are more in line with their racial character flavor-wise, like f.ex. the Sunwalker as the Tauren version of the Paladin. These class variants are still rather close to the baseline class to avoid controversy due to an unwanted change. Races with a specific class variant are written in italics.
• Race-specific new baseline (optional): this is the chicken version of the race-specific replacement - a new class variant is introduced, but the baseline version isn't ineligible. So for example it's possible for an Undead or a Gnome to play a standard Hunter, despite the new baseline version being the Forsaken Dark Ranger or the Gnome Tinkerer.
• Race-specific class names: this is the most minor of changes - the class as such doesn't get modified, but it gets a new name that's more in line with the lore; examples being the Draenei Vindicator or the Tauren Spirit Walker (race specific class names are written in parentheses). If race/class specific titles as a reward are introduced, this point is redundant.
• Additional race-specific varieties: this is the ultimate way to make classes accessible to more races - if a baseline class is restricted to this race, a class variety is chosen that's more in line with that race's character (the Goblin Alchemist could also work as a Shaman-variant for Gnomes, for example; or the Sentinel Priest being the Paladin option for Night Elves). If necessary, this can be expanded to all race/class-combinations with a bit of creativity.

Class variants

Ranger (Hunter)

The Ranger class is a ranged class, accompanied by a pet.

Hunter:

• The Hunter is identical to the existing class, the only difference being that it's now considered a sub-class of the Ranger.
•  Specializations: %
•  Races: Humans, Dwarves, Night Elves (Sentinel), Worgen, Draenei (Rangari), Orcs, Tauren, Trolls, Blood Elves (Ranger), Pandaren

A Gnome Tinkerer.

Tinkerer:

• The Tinkerer is a more steampunk-like variety of the Hunter. The Tinkerer relies on muskets and shotguns instead of bows, uses mechanical traps and other devices and is followed by constructs and other mechanical pets instead of animals and beasts.
•  Specialization: Gunnery (Marksmanship), Mechanics (Beastmastery), Melee (Survival)
• Races: Gnomes, Goblins, Dwarves

Dark Ranger:

•  The Dark Rangers are the archers of the Forsaken. Unable to command the loyalty of living animals, they harness necromantic powers instead and are followed by undead creatures - or mindless humanoid thralls. 
•  Specialization: Archery (Marksmanship), Domination (Beastmastery), Survival (Survival)
•  Races: Undead

Wizard (Mage)

The Wizard is a class that relies on wielding raw magic energy to cast direct-damage spells.

Mage:

• The Mage is identical to the existing Mage class; the only difference being that it's now considered a sub-class of the Wizard.
•  Specializations: %
•  Available to: Humans, Dwarves, Gnomes, Night Elves, Worgen, Draenei, Trolls, Forsaken, Goblin, Blood Elves, Pandaren

Sorcerer:

• The Sorcerer taps into darker sources than the elements or the arcane - ultimately, it's a Mage with the look & feel of a Warlock. The specializations are fel fire instead of fire, void energies instead of arcane, and curses and tentacles instead of ice.
• Spezialications: Fel (Fire), Entropy (Ice), Void (Arcane)
•  Available to: Humans, Gnomes, Dwarves, Worgen, Orcs, Blood Elves (Blood Mage), Forsaken

Summoner (Warlock)

The Summoner class relies on calling other entities to help him and uses debuffs and DoTs.

Warlock:

• The Warlock is identical to the existing Warlock class, the only difference being that it's now considered a sub-class of the Summoner.
• Specializations: %
•  Available to: Humans, Gnomes, Dwarves, Worgen, Orcs, Blood Elves, Forsaken

Necromancer:

• The Necromancer is a Warlock variety that's more molded after its equivalent units in WC3 (Lich and Necromancer) and WotLK. The main differences are that it uses frost and shadow magic instead of fire and necromancy instead of demonology; and summons shades (imp), ghouls/skeletons (voidwalker), banshees (succubus), skeletal mages (fel Hunter) abominations (fel guard) and revenants (doom guard) to his aid.
•  Specializations: Curses (Affliction), Frost (Destruction), Necromancy (Demonology)  
• Available to: Humans, Gnomes, Dwarves, Worgen, Orcs (Necrolyte), Trolls, Blood Elves, Forsaken

Hexxer:

• The Hexxer is more akin to an even darker form of the Loa Shaman, who doesn't use his powers over the spirit realm for beneficial ends, but to enthrall the ghosts of the dead and weaker loa and demonic entities to acquire greater power. This class uses otherworldly fire and shadowy curses as the normal Warlock does, but summons shadow spirits (imps), animal skeletons (voidwalker), possession spirits (succubus), totem spirits (fel hunter) and Loas (doom guard) to his aid.
•  Specializations: Hexes (Affliction), Destruction (Destruction), Spirits (Demonology)
•  Available to: Troll

Paragon (Paladin)

The Paragon is a plate-wearing melee class that wields light-based magic. This class captures the martial factions of all cults devoted to some form of the Light, whether it's the Holy Light (Humans and Dwarves), the Naaru (Draenei), the Sunwell (Blood Elves), An'She/the sun (Tauren) or Elune/the moon (Night Elves).

Paladin:

• The Paladin is identical to the existing Paladin class, the only difference being that it's now considered a sub-class of the Paragon.
• Specializations: %
• Races: Humans, Draenei (Vindicator), Dwarf (Warrior Priest)

Sentinel Priest:

• They would be the latest addition to the Silver Hand (with Delas Moonfang as some sort of alpha test) should they get introduced. The Night Elven Sentinel Priests are similarly to the original Paladins an offshoot of their race's Priestclass, and as such wielding moonlight-based holy magic to heal and augment their attacks.
•  Specialization: Avenger (Retribution), Moonlight (Holy), Warden (Protection)
•  Races: Night Elves

A Tauren Sunwalker.

Sunwalker:

• As the "least civilized" race among those inducting Champions of the Light and originally conceived as a sun-oriented counterpart to the Druids, Tauren Sunwalkers use a more naturalistic approach to the light than their comrades from other races. Because of this, Tauren should be (as opposed to the other Paladin variants) the least like knight templars and, if anything, more like barbarians.
• Specializations: Avenger (Retribution), Sunlight (Holy), Protector (Protection)
•  Races: Tauren

Blood Knight:

• The Blood Knights are an order of Magic Warriors who channel the power of the Light for their purposes which are violent more often than not. Only loosely affiliated to the Silver Hand, are more akin to a mix of Warriors and Mages than Warriors and Priests.
• Specializations: Vengeance (Retribution), Sunwell (Holy), Blood (Protection)
• Races: Blood Elves

Primalist (Druid)

The Primalist refers to a class that can change shapes at will and uses nature-based magic for healing and dealing damage. The Primalist class remains unchanged for the Tauren and Night Elf Druids - both races have a long history within the Cenarion Circle and as such have similar traditions and rituals, with the Tauren essentially having adopted those of the Night Elves. However, this doesn't have to apply to the other races who (despite the efforts to shoehorn them into the baseline Druid tradition) would actually have offered quite interesting interpretations of this class on their own.

Druid:

• The Druid is identical to the existing class of the same name, the only difference being that it's now considered a sub-class of the Primalist.
•  Specializations: %
• Races: Tauren, Night Elves

Shapechanger:

• As a lycanthropy-powered class, they transform into wolflike beasts: instead of a cat, they're using a feral worgen form, a mix of the standard worgen form and a wolf prowler; and instead of a bear, they're morphing into a giant hulking werewolf. Their travel form is that of a wolf mount (without a saddle), their flying form is a bat-like animal. Their healing magic functions as bestowing their regenerative abilities on others (nature-type healing), while their arcane magic is them tapping into their connection to the moon. They're using a modified standard Worgen form for either of these specializations.
•   Specializations: Protector (Guardian), Prowler (Feral), Regeneration (Restoration), Lunar (Balance)
•   Races: Worgen

The Worgen Shapechanger.

Loa Primalist:

• One of the three branches of the Loa Priesthood, the Primalists are those who are most in touch with the primal, animalistic nature of the Loa spirits. Like their distant kin in Zul'Gurub, Zul'Aman and Zul'Drak, they have managed to master the form of their spirit animals, although in a less powerful (but also less exclusive) way. Unlike the Worgen shapechangers, their connection to the actual Druids from the Cenarion Circle is tenuous at best, as is their connection to the moon/Elune. Jungle Trolls transform into a sneaky raptor form, a mighty tiger, a flying snake using lightning and arcane magic, or a bipedal lizard using regenerative nature-type magic; and use totems to support their casting.
• Specializations: Tiger (Guardian), Raptor (Feral), Serpent (Balance), Lizard (Restoration)
•  Races: Trolls

Naturalist (Shaman)

As mentioned, the original Shaman was essentially a merger of all existing horde units from WC3 that were spiritually or magically oriented. This basically resulted in a gestalt class where a Shaman got access to all the flavors of all classes at once - casting lightning blasts like an Orc, linking spirits like a Tauren and dropping totems like a Troll. As if this hadn't been enough, this class was introduced to other races whose spiritual traditions were actually pretty far removed from the traditional horde Shamanism (Dwarves, Draenei, Goblins, Pandaren).

The Naturalist is an attempt to reconcile these contradictions with one another. Essentially, the Naturalist is a class that bends the elements to his will in one way or another or imbues himself with their powers. Totems (as an optic effect) are removed form the Naturalist's portfolio (unless you are a troll) and are replaced with functionally identical but visually different ways of placing AoE spells.

Shaman:

• The Shaman is almost identical to the existing class of the same name, the differences being that totems are removed in favor of mechanically identical spells/effects and that it's now considered a sub-class of the Naturalist.
•  Specialization: %
• Races: Orcs, Tauren (Spirit Walker)

Loa Shaman:

•  The Troll Loa Shaman is similar to the existing Shaman class, the difference being that it's  considered a sub-class of the Naturalist.
•  Specialization: Berserker (Enhancement), Shadow Hunter (Elemental), Restoration (Restoration)
•  Races: Trolls

Scientist:

• Since Goblins are hardly a race that is attuned to nature, envisioning them as a Shamanistic race feels oddly out of place. The Goblin Scientist is insofar different from all the other class variants on this list as he doesn't rely on the power of the spirits and the elements to do his bidding, but uses chemicals and potions to both empower himself and heal others, as well as using lethal energy-generating devices to shoot blasts of elemental power.
• Specialization: Concoctions (Restoration), Infusions (Enhancement), Devices (Elemental)
• Races: Goblins

The Goblin Scientist.

Titan Priest:

• The Titan Priest also is a significant step away from the Shamanist archetype as the spiritual leader of a race in touch with nature; and more devoted to the Titans and their Titanic Watchers who hold dominion over the elements, harnessing their powers to similar ends.
• Specialization: Weaponry (Enhancement), Might (Elemental), Healing (Restoration)
• Races: Dwarves

Sage:

•  The sage is a specific type of Naturalist that is less like a tribal character and more a character that's spiritual as well as martial, a healer who uses mystical energies and is skilled at dual-wielding. A sage is, so to speak, a Naturalist who has the look and feel of a Monk.
•  Specialization: Martial Mastery (Enhancement), Serenity (Restoration), Energy (Elemental)
•  Races: Pandaren, Draenei

Adept (Monk)

The Spiritualists are a class of wise men, bare-handed melee fighters and dedicated healers. Some, like the more civilized races, have created monastic orders to train these martially inclined clerics, others revere barbaric hermits whom they consider holy men.

Monk:

• The Monk is identical to the existing class of the same name, the only difference being that it's now considered a sub-class of the Adept.
• Specialization: %
• Races: Pandaren, Gnomes, Undead 

Cleric:

• The Cleric is a more "occidental" take on the Monk, who wields the Holy Light instead of spiritual energies.
• Specialization: Staffmaster (Brewmaster), Crusader (Windwalker), Healer (Mistweaver)
• Races: Humans, Dwarves, Draenei, Night Elves, Blood Elves 

Spiritualist:

• Spiritualists are holy men - barbaric hermits who are in tune with the spirits, but are still raging Warriors if their tribe calls for them. If the Sage is a Shaman with the look and feel of a Monk, then the Spiritualist is a Monk with the look and feel of Shaman.
• Specialization: Stonewielding (Brewmaster), Berserking (Windwalker), Restoration (Mistweaver)
•  Races: Orcs, Trolls, Tauren

Priest

The Priest is merely the class of the spiritually attuned. While most races with priests revere the Light in one form or another, some actually draw their spiritual energy from other sources.

Priest of the Light:

• The Priest of the Light is one of the new baseline classes. While he's mostly like the original priest, he doesn't use shadow magic any longer, but resorts to the energies of the netherlight instead.
• Specialization: Holy (Holy), Discipline (Discipline), Netherlight (Shadow)
• Races: Humans, Dwarves, Draenei (Anchorite), Night Elves (Priest of the Moon), Worgen (Priest of the Moon), Tauren (Sun Priest), Blood Elves 

Priest of the Dead:

•  The sinister priesthood of the Dead are a shadowy cabal who don't revere the light, but otherworldly powers with connection to the afterlife that bestow their abilities on them.
• Specialization: Flame (Holy), Death (Discipline), Shadow (Shadow)
•  Races: Forsaken, Orcs (Pyremaster)

Alchemist:

• Like the Goblin Scientist, the Alchemist is yet another more mundane take on a generally spiritual character.
• Specialization: Potions (Holy), Barriers (Discipline), Poisons (Shadow)
• Races: Gnomes, Goblins

Mystic:

• The Mystic is in a way the inverted version of the Cleric - a Priest that appears like a Monk; however, he's ultimately closer to what would be a Psionic.
• Specialization: Spirit (Holy), Meditation (Discipline), Psychic Force (Shadow)
• Races: Pandaren

Witch Doctor:

• The Witch Doctor is, in a way, a mix of the Loa Shaman and the Hexxer. Unlike the other priests, the Witch Doctor resorts to nature magic to cast his beneficial spells, and taps fully into the dark arts for his more aggressive magicks, and uses totems for certain effects
• Specialization: Restoration (Holy), Spirit Warding (Discipline), Hexes (Shadow)
• Races: Trolls

The three spiritual classes of the Trolls: Witch Doctor, Loa Shaman, Loa Primalist.

Warrior and Rogue / Death Knight and Demon Hunter

These classes remain unchanged (except maybe for class names), the former because they - as the most archetypical classes - are truly general; the latter because they're already unique hero classes (though the baseline game mechanics would also be adaptable to other classes one would have to come up with).

Further questions regarding class varieties:

• Further class varieties: Given the fact that classes are essentially reduced to their game mechanics, this opens up all classes and units from the Warcraft RTS-universe as valid options, as long as one gets creative enough. An example would be the Blood Elf Spellbreaker - it's quite possible to shoehorn that unit into the Death Knight-mechanics.
•  Racial flavor: Another option would be differentiating the same sub-class for the races it's available for - especially in those cases where a separate sub-class isn't warranted, but where slight differences are nevertheless present. An example would be the Blood Mage who might use different demons than the baseline Warlock, or the Priest of the Moon who would use moonlight for his spells instead of daylight like the regular priests. An additional example would be naming all classes differently, even when they're identical in every other respect (this has already been done with certain Sub-classes like the Necrolyte, the Vindicator etc.). 
• Which sets for which class:  That's admittedly trickier. The easiest option would be to either slightly modify the sets that get introduced from now on (different colors, possibly a few additional adornments etc.) or to use a variety of the set of another class (like, say, making similar armor sets for Death Knights and Necromancers; or giving the Warlock and the Sorcerers similar sets etc.)
•  How to deal with class quests/order hall quests: A possible solution here would be to move away from classes and move to themes instead. For example, the Mystic and the (classic) Monk would use the same campaign, like the Necromancer and the Dark Knight, the Sorcerer and the Warlock etc.