Warlocks were inspired by Demon Hunters from the very beginning. Was it every in doubt that the Warlock draws inspiration from the class? It took spells from the Demon Hunter, Pitlord, Dreadlord - and even Death Knight. When they designed WoW's classes, they focused on taking what familiar and iconic abilities there were and allocating them to appropriate classes to fill out a broad spectrum. They didn't have Hero classes in mind, that's why a spell like Death Coil was first given to Warlocks, which was retroactively changed when the actual Death Knight class was introduced.Immediately following that, Warlocks started getting Demon Hunter abilities.
Demon Hunters aren't evil. Illidan fell to his own pride, going full-blown demonic. There's really nothing to say that the Demon Hunter champion for the Player Class will go in a new, better direction that fits the Alliance and Horde. And if Illidan does return, he will likely have a redemption or revenge story, where he goes back to being a classic Anti-Hero instead of pure villain. I don't see Blizzard making Kerrigan 2.0 out of him. He's a damned cool character, but he doesn't need to be tied to the playable class. I mean look at Chen Stormstout; we have playable Monks and none of them have anything to do with him.A "redemption" story for DHs sounds kind of silly. It makes since for DKs because they're fallen champions. Demon Hunters actively choose to embrace the darkness of demonic magic (just like Warlocks).