that brings up another point: I firmly believe that Illidan is dead, slaughtered, got his ass pwned by arthas, whatever. There are people saying he's still alive, but I think that would be a really cliche and stupid move for Blizzard. Arthas kills Illidan. Final cinematic in TFT. We all saw it. Now why contradict it? Aside from that: Blood Elves are no longer connected to the alliance because they have tapped dark magic, and have ben shunned and outcasted and spit on. /spit blood elves.
The draenis excuse is the worst though. but it makes sense, maybe. Archimonde and Kil Jaeden are both draeni, but they were tempted and corrupted by the previous leader of the burning legion Sargases (sp?). Anyway, the remaining draeni that did not succumb to his corruption fled and landed in outland and settled there. A group of "angelic like" beings helped them to get there and to help keep them safe from the burning legion, which was ever hot on their trail, so they decided to follow the light, very similar to this stupid bloody pallys you will find in WoW. /moon pally.
As well: It wouldn't make any sense for draeni to ally themselves with the horde because the orcs like totally destroyed them when they got there. As for a third faction, 2 is enough for me, and plus: naga and illidans forces will ALWAYS be just a neutral race. helping whoeveer they feel, but not starting anything either.