Now i've always loved the idea of Illidan coming back, and all these speculation threads are getting me hopeful however, one I thing I havent seen mentioned much, is the hint from the warlock green fire questline, suggesting that illidan might not actually be dead, the follow is dialog from that part of the quest:
Ruins of Farahlon Memory
Jubeka Shadowbreak: Such strange creatures. Why do they remain so long after the legion has left?
Kanrethad Ebonlocke: … there’s a slight flaw in that supposition.
Jubeka Shadowbreak: Oh?
Kanrethad Ebonlocke: The Observers were in the service of Illidan … not the legion.
Jubeka Shadowbreak: Well, he’s gone too … so why are they still around?
Kanrethad Ebonlocke: How should I know?
Thoughts? is there someone else controlling these demons? is Illidan licking his wounds? I want him back, even if we don't get demon hunters but eh, fire away