Dont hold your breath. I seriously doubt there will be WoW2. Why make another MMO when you can make cheap games like Hearthstone or Overwatch which will bring in comparable money at fraction of the production cost?
I can see them continuing to cut parts off WoW (so to speak) and making them into separate titles. Overwatch is WoW's battlegrounds (kind of) so maybe a hub based multiplayer dungeon game is next.