Would you bring back the Scourge for yet another expansion, create an entirely new enemy, focus on the Alliance versus Horde conflict, or something entirely different and "Outlandish"? For those of you who really don't care about the story or lore, it still determines what your gear will look like, what continent you're going to be leveling on, and what sort of races and classes you'll have access to.
Personally, I'd love to see a spacefaring expansion or an expansion that focuses entirely on the present conflict between the Alliance and Horde. Mists of Pandaria claims to focus on this conflict, as there seems to be no "Big Bads" or supervillains present, and I think that's a step in the right direction. Still, Pandaria serves as a distraction from what could have been an amazing story of war between the Alliance and Horde. I think Blizzard gives too many shining moments to the good guys and has a difficult time creating believable villains. Most importantly, I think Blizz has a difficult time creating villains you can easily sympathize with. Their story department can't seem to create a villain that I would say, "Wow, he's actually right," to. I like villains when I can agree with their ends but have a few problems with their means, and so far, Blizzard has really only developed a caste of villains who want to "DESTROY EVERYTHING!!!" I can't get behind that kind of idea for obvious reasons.
I have a feeling that the "Sha", or the "Elemental Hate" is going to give this expansion a reason to end on a happy-go-lucky "We're the heroes of Azeroth" note; I don't want to be a hero, I want to be a player in a global conflict. This upcoming Mists of Pandaria expansion will end with the Pandaren tying the Alliance and Horde together with their lessons of kindness and peace, and the Horde and Alliance will eradicate the Sha, or the Elemental Hate, and learn to love each other. I hate to say it's going to end that way, but it is. I'll put 50 bucks on it right now. The story will start off with the Alliance and Horde plunged into absolute and total war with the destruction of Theramore, and for a moment we'll finally get to see these two great civilizations and their member states unleashing their most terrifying weapons. That will end soon when Blizzard's wise, Monk-like race exerts their international influence through their new Monk cadre and the fact that there are great number of Pandaren amongst the Alliance and Horde, when they will then stop the conflict with the power of love. Tell me I'm wrong, because I don't want to be let down.