While roaming around the blood elf starting area in the middle of the night, I got into a discussion with some other neophyte elves about Illidan. Basically, we didn't want to kill him.
See, Kael'Thas is rumored to have gone insane, and Vashj was never too good in the first place, but Illidan ... well, what Illidan says in the Burning Crusade introduction is pretty accurate. He was locked up for thousands of years for being reckless, was nearly killed trying to kill the totally evil Arthas, and then when he finally gets to Outland and is able to relax, millions of warriors invade his country from Azeroth to look for his loot. He doesn't seem to pose much of a threat to Azeroth, so why is it so important that we metaphorically and literally break into his house and rummage through his stuff? Illidan's admittedly many mistakes (creating a new Well of Eternity, consuming Gul'Dan's skull, dealing with Kil'Jaeden) were made out of recklessness and selfishness, not outright "Yay, let's destroy the world!" evil. There have been quite a few forum posts on the same subject.
My fellow blood elves suggested that we be given the opportunity to ally with Illidan and his crew. To join them, you would have to forsake your allegiance, your homeland and your faction. You could still communicate with your old friends, but you wouldn't be able to group with them. You'd have different profession recipes, quests, towns, and maybe even different talent options. One even suggested that we could be double agents - we could still hang out in Orgrimmar or Ironforge, but have a chance to be detected and permanently cast out and maybe even lose some items.
The instances could change too. Instead of fighting Illidan in the Black Temple, you could defend him from Kil'Jaeden's minions. And who says we have to preserve the timeline in the Caverns of Time? That's boring. Let's see what happens if Archimonde wins the battle of Hyjal and Thrall dies as a kid!
Of course, that isn't going to happen. World of Warcraft is a pretty static world and you don't have many real character development options. The one big one we do have - the ability to go to war with factions - has caused enough complaints (see: Bloodsail pirates angry about goblin questgivers) and this isn't the Elder Scrolls series. Still, it's fun to speculate about.
Then again, maybe Illidan is right, and we're just not prepared.