The Lich King
Which would tie into a Burning Legion expansion quite well, and make him able to train new demon hunters.
Hell, we could also have Alleria Windrunner (3rd Windrunner sister) teach you another spec, Dark Ranger, since she too is trapped in the Twisting Nether, as is Anduin Lothar, who is more of a warrior than a Paladin (Sons of Lothar faction in Outland was an homage to him).
Which would make the new class for that expansion something like Purifier with Dark Ranger / Demon Hunter / XXXX Specs. Maybe 3rd one could be a type of Holy Paladin but with another way of playing.
Last edited by Pickwickman; 2013-02-21 at 05:36 PM.