As I wrote over at TAGN, what the next expansion should be, but won’t because this is New Blizzard, is an expansion of garrisons, with Blizzard taking one of the current most successful games (Clash of Clans) and doing what Blizzard did best; copy/paste + apply Blizzard coat of paint.
Garrisons should be expanded to be used in the same way a base is used in CoC. You set up its layout to defend, and your followers become your troops that attack. Via questing, crafting, raiding, and battlegrounds, you can collect resources to upgrade both your defenses and followers, and your overall garrison has an ‘iLvl’ like your character.
You would initiate a search for a base to attack, be able to skip to another until you find one you want to hit, and then the attack would play out much like it does in CoC; you can’t directly control your followers but they have different AI with different focuses (some target defenses, others resources, etc). Since WoW is focused around a character, you can also use your character in the fight as a kind of super-minion, with customizable AI.
Add in a ranked mode, along with guild vs guild wars, and you have something that ties a lot of the existing WoW content into this new ‘end-game’ feature, allows you easy expansion (more defenses, more followers, more skins for garrisons/followers) without having to create new zones, more character levels, or dungeons/raids that would go stale once someone has the items they want.
But knowing New Blizzard, the expansion will just be more orcs or something equally dumb.