Expansion Theme II: History of Azeroth

This idea to make old story content interesting and engaging would be to use it as a blueprint for new expansions that take place in days gone by. An example for a straight execution of this story concept would be a spinoff that takes place in the old days of Warcraft 2: Tides of Darkness.

Races & Classes

The Alliance of Lordaeron

•  Humans: standard
• Dwarves: Dwarves are basically like they were in Vanilla WoW - except that players can choose between classic Ironforge Dwarves (like vanilla WoW Dwarves) and Wildhammer Dwarves who start at Aerie Peak.
• Gnomes: standard
• High Elves: The High Elves have different racials than the Blood Elves and don't have access to Paladins, but do have access to Warriors instead.

 “The mysterious Elves of Silvermoon have sent a contingent of Archers south to survey the supposed orcish threat for themselves…”

The Horde

• Orcs: Given the fact that Orcs are still aligned with the Burning Legion, they don't have access to Shamans yet (or Dark Shamans like in WoW:MoP).
• Forest Trolls: the bulkier and more feral brethren of the Jungle Trolls. Technically identical.
•  Goblins: standard
•  Ogres:...

Generally: No Death Knights, Demon Hunters, Monks and Druids.

 Zones and Realms

The entire spinoff would take place exclusively in Azeroth as it was around the time of the Second War, prior to the Rise of the Scourge and the Retaking of Stormwind.

Quel'Thalas

• Eversong Forest (Eversong Forest & northern part of the Ghostlands): The Eversong Forest is still standing in all its splendor, and so is Silvermoon City in its entirety. However, the realm is under constant attack by Troll/Orc raiding parties.
• Zul'Aman (southern part of the Ghostlands): Zul'Aman is situated south to the Elven realm, having pushed back the Quel'Dorei incursions of the past thanks to their orcish allies. Zul'Aman is also place of one of the largest wharfs of the Horde, where the Troll Destroyers set sail.

The Human Kingdoms

•  Lordaeron & Tirisfal Glades: A more vivid, lively area, mostly dominated by Lordaeron City which is far larger than Undercity (around the size of Stormwind) and extends into the Northern Parts of Silverpine Forest. The Scarlet Monastery is still a place of the cult of the Holy Light at that point.
• Darrowmere Region (Western Plaguelands): The breadbasket of Lordaeron for the northern communities, with Andorhal in its center and Hearthglen (back then still a
• Eastweald & Darrowmere Forest (Eastern Plaguelands): An area of thick forests where beasts and brigands roam, with the proud city of Stratholme and the passageway to the Elven Kingdom to the north and Tyr's Hand to the southeast. It looks mostly like the CoT3 (Culling of Stratholme) instance.
• Gilneas & outskirts: The recluse kingdom of Gilneas, hidden behind the Greymane Wall and ruled by its namesakes. At this point still readily accessible, the kingdom of Gilneas nevertheless looks very much like the Gothic city of WoW:Cataclysm. Except without Worgen.
• Silverpine Forest: Similar to the area in the original game (except not as gloomy), the Silverpine Forest is an area roamed by brigands and the henchmen of the enigmatic sorcerer Arugal).
• Alterac, Dalaran & Hillsbrad Foothills: A densely populated area, the Hillsbrad Foothills are the region where the magocracy of Dalaran, the city-state on Cross Island, the city-state of Alterac and the twin villages of Southshore and Tarren's Mill are situated. Apart from the fact that the two cities are still standing, it's mostly like the original Hillsbrad, though.
• Stromgarde & Arathi Highlands: Stromgarde is still standing, with the Trollbane kings still in power at that point. A contested land where the orcish Horde is in a constant struggle with the armies of Stromgarde, it nevertheless is very similar to the standard Arathi Highlands.
• Tol Barad: A normal questing area instead of a battleground, with Stromgarde still in charge.
•  Kul'Tiras: The island realm of Kul'Tiras.

The Dwarven Realms

• Hinterlands: Jintha'Alor may or may not be Horde-affiliated at that point, with the Wildhammer Dwarves being their opponents. Otherwise, still like the standard Hinterlands.
• Wetlands (western part of the Wetlands): contested between the Dwarves and the Orcs; with Menethil Harbor being crowded by refugees from the kingdom of Azeroth.
• Grim Batol & Northeron (eastern part of the Wetlands, Twilight Highlands): The center of the Wildhammer culture, with their capital at Grim Batol. The Twilight's Hammer has already intruded into this area, at the time still affiliated with the Horde.  
• Ironforge, Gnomeregan & Dun Morogh: Like the standard questing area, except that Gnomeregan is still standing. 
• Loch Modan: Like classic Loch Modan.
• Searing Gorge: Like the classic Searing Gorge, ruled over by the reclusive and hostile Darkiron Dwarves, the difference being that the presence of the Blackrock clan is far stronger here.
•  Badlands: Like the Searing Gorge, except more draconic presence.

The Orcish Empire

•  Burning Steppes: With Deathwing still in league with the Horde, this area is ruled over by Orcs from the Blackrock clan and has less draconic presence.
• Westfall: Like classic Westfall, except with Orcs instead of Defias, and the Deadmines being one of their harbors.
•  Elwynn Forest: Like classic Elwynn, except that all Human settlements are in ruins and the Horde is stripping the area of its resources, being constantly attacked by the Gnolls.
• Ruins of Stormwind: Utterly devastated, a testament to the might of the Horde. The Humans here are broken shells, toiling away in slavery.
• Duskwood: Home to the ruins of the town of Grand Hamlet, this area is less gloomy and gothic than the original Duskwood.
• Redridge: Like the original Redridge area, except without a Human village and a stronger Horde presence (who are occupied with fighting off the Gnolls).
• Swamps of Sorrow (Swamps of Sorrows & northern Blasted Lands): the putrid swamps of sorrows with the twin villages of Rockard and Stonard. Nethergarde isn't built yet, and the swamps extend further to the south. Atal'Hakkar is still sealed, and the Alliance is notably absent.
• Blasted Lands (southern Blasted Lands): The area around the Dark Portal, with a strong Dragonmaw presence and plenty of enslaved red dragons in the sky. Partially under water.

The Deep South

•  Stranglethorn Vale: Like the original Stranglethorn, except with a stronger jungle Troll presence, and the starting area of the Goblins in the South.

Due to the nature of this spinoff (which is more focused on the fact that Azeroth is still divided between the two factions than being overwhelmed by hostile neutral factions), most raids or instances would be required to have different but equal encounters - think of the arena fight in TotC or the third encounter in ICC.

• Ruins of Stormwind: Alliance players raid Stormwind and kill the Horde commander, Horde players crush down a Human insurgence.
• Hoard of Alexstraza: Alliance players defeat a controled Alexstraza in order to free her from the Horde's mind control, Horde players defeat a free Alexstraza in order to bring her under their spell.
• Invasion of Zul'Aman: Alliance players invade Zul'Aman (starting from a High Elf camp), Horde players drive back an Elven invasion.
• Battle for Silvermoon: Like Invasion of Zul'Aman, only with switched roles and taking place in Silvermoon.
• …and so on.

Expansion themes I: General

A few ideas not about game mechanics and how to improve them or about how to make the game more appealing/addictive, but simply about possible sorts of content: Even though I assume that there are plenty of other possible expansion themes going around, I wanted to suggest a few other ideas.

• Steampunk: A steampunk-themed expansion would pick up on several elements the game has already touched upon in the past, but this time it would be central to the player effort. The Legion, the Titans and the Iron Horde all used retro- and retrofuturistic-looking machinery, but the Alliance and Horde war effort was generally carried by high fantasy (with the medieval-looking Alliance) and sword & sorcery (with the  barbaric Horde) themes. A steampunk expansion would put the more technically and less magically oriented factions in the center, like Gnomes, Dwarves, Goblins and (Iron Horde-like) Orcs; and the world should also reflect that theme: war-torn areas that look a lot like Northern Gorgrond, naval battles with advanced ships like in late WoD, Gnomish clockwork cities and Goblin factory towns, Dwarven mountains and secluded Titan fortresses, Legion robots instead of dragons and demons.

 

Steampunk, Orc-style.

• Timegate: While the WoD expansion was less than optimal when it came to storyline coherence (for example: when Garrosh travelled back in time in a parallel timeline, why did he attack today's Azeroth and not his contemporary Azeroth from 35 years ago?), and was obviously mostly done to capitalize on the popularity of the Horde-related Warcraft lore, an actual timegate expansion would put the time travel aspect present in the game into its center instead of just using it as an excuse to enable the players to see Draenor in all its former glory. This of course would also mean that the Bronze Dragonflight as well as the infinite Dragonflight would play a central role this time. The timegate expansion would put the Caverns of Time into its center and would allow the player to visit various places from Azeroth’s past. It would be less a “continent expansion” (like all expansions except Cataclysm), but one of several “islands in the sea of time” where players are enabled to visit defining moments of history and have to come up with various ways on how to save the world. Think of Chrono Trigger and you have an idea of how it might look like. 
•  Gothic: In that scenario, the world would have a vaguely Victorian flair, not unlike Gilneas; and the center would be the Worgen and Undead factions. People running around with a wardrobe similar to that of the time (expect to see a lot more monocless, glasses, coats and firearms), cities are gloomy and convoluted, magic comes more in the form of witchcraft and sinister covens than of glamorous Elven sorcery. The enemies are likewise: Lovecraftian horrors would make the Void Lords a fitting villain for that story. 

Gothic, Worgen-style.

• Race-themed: Delving deep into the lore of a specific race and making this the background of the expansion. This has already been done in BC (Draenei, Orcs, Blood Elves), WotLK (Humans, Dwarves, Gnomes to a lesser extent, Undead), Mists of Pandaria (Pandaren), Warlords of Draeneor (Orcs, Draenei), Legion (Elves in general, Draenei), but a considerable amount of races have been ignored so far.