Assumption makes an ass of you and me; though in this case, primarily you. I don't know where you get this notion that by me saying "last expansion", I mean the end of the game. With expansions come patches and frankly if the next expansion is to deal with the Burning Legion, which I wouldn't consider unlikely, then there really aren't too many enemies in the game left to deal with; or rather, enemies that would need an entire expansion dedicated to them. The Burning Legion has and always will be the biggest threat in WoW; moreso than Old Gods, Naga or other things, and once they're dealt with then I see no reason why the rest can't be in major content patches.