Well based on Metzen seemingly becoming hyper excited when asked when we will see Illidan's redemption and resurrection on BlizzCon 2010 i think it's safe to say he'll be back in...an expansion or WarCraft 4. Then there's also the fact that Illidan is one of the most popular WarCraft heroes and Blizz has an addiction to corruption and redemption themes and it's passed due for Illidan to be a badass that isn't always being shown as a bad person. What are some peoples thoughts on this though? How do we think Blizzard should handle the character? I think they honestly did him some disservice in BC in how he was as a character. IMO, the Titans may very well be the reasoning behind his return. It's hinted that the Old Gods used and corrupted Illidan to their own goals. Considering Illidan has been "marked" for greatness since birth it would make sense that he has the capability to be a 'champion' of sorts for the Titans. Why not make a Demon Hunter class with his resurrection for WoW (if done so in WoW). However for the Titans im sure at this point they must be taking notice of the events on Azeroth. Their old machines are acting up Old Gods stirring and Sargeras is well...who knows what that nut job is doing. I personally dont think the Titans will play a direct intervention easily so why not resurrect/purify/heal Illidan train him/give him power/knowledge and have him and his Demon Hunters be not only a counter to Old Gods but to Sargeras as well - Demon Hunters that answer, in the end, to the Titans themselves.
But that's just one possible way in my head they could do it. In the end I just hope they bring the badass back and no more "zomg you preserved magic by making another well of eternity thats now mount hyjal and the sunwell two major sources of powerrrr. and like zomg your taking in all this power to save our livezzz you so baaad illidan!!!"