What about Thassarian standing there near Amal'thazad? There was a quest in WotLK with him interrogating another Lich named Tanathal. When you click him he says "We must set aside our differences and work united if we are to defeat the demons. The fact that he dont seem to like Lich Lords but is willing to work with one(Amal'thazad) for the greater good, I was thinking that maybe having him as a combat ally might trigger something? Probably nothing but I found it interesting