The two that come immediately to mind are the Netherwing Dragonflight and the Ashtongue Deathsworn. What's up with the Netherwing since Deathwing's demise? Do they even know about it or what's happened with the Aspects? And what's going on with Akama now? I'd argue that he, more than Kael or Vashj or Illidan, was the greatest and most compelling character of WoW's first expansion, and he had one hell of a unique model. The brains behind the Ashtongue's high-stakes Batman Gambit (warning: TV Tropes link) has got to be up to something these days, and if Blizzard ever revamps Outland questing, I hope it gives players a peek.
Then again, that's assuming that yanking Illidan back from the dead is even a good idea to begin with (is it?) or that Outland stories can be made relevant to their modern counterparts. Thoughts, readers?