There obviously can't be any winning side at all, because it would indeed be the end of the world. Of Warcraft. With that consideration, I don't see any problem with having a Burning Legion Faction. It would add an interesting dynamic to existing battlegrounds -- "which side are we going to be up against in this one?"

And for all that warlocks are cool, they've always been incongruous as PCs since they're obviously agents of the Burning Legion. They have no other agenda for wielding fel magic and summoning demons. What, to further their own ends? Dream on. Them powers and demons don't come cheap.

And Matt, it sounds like you've not read Wolfheart. The Worgen joining the Alliance wasn't simply at the behest of the Night Elves. There is a spiritual bond between Wrynn and Greymane, and Tyrande is in awe of Wrynn because he is an avatar of Goldrinn. Nor are the Draenei just lapdogs to the Night Elves -- guess where the future ruler of Stormwind has gone off to college. No, the Alliance is just fine, thanks.