I'm sorry for the vagueness and overall badness of this thread. Even I despise it. But I've got to share my point and I'm too lazy to go into detail.
Basically I had this crazy idea for a future bit of lore regarding the invasion of the Burning Legion and the Lich King.
So, Kil'Jaeden was the one that originally tore up Ner'zhuls soul and put it in the Lich King armor, so I'd imagine that right now, if he still exists, Ner'zhul would be pretty pissed and want some revenge on Kil'Jaeden for doing that to him and imprisoning him on Azeroth. If the Legion were to return to Azeroth lead by Kil'Jaeden, would it not be pretty cool for that somehow to tie in with the Lich King/Bolvar story?
Like, it's tricky because Bolvar currently has control over Ner'zhul and he is keeping the Scourge at bay. But maybe if Kil'Jaeden did return to Azeroth, Bolvar and Ner'zhul could unite for the same cause, to bring down the Burning Legion and Ki'Jaeden, and use the Scourge as the ultimate weapon. We could have a good Lich King trying to help us defeat a common enemy and Bolvar could maybe return a hero to the Alliance.
JUST AN IDEA