.  Naga expansion, with either N'Zoth, the Old God theorized to be the one below the Rift beneath the Maelstrom, or Azshara as the final boss. If N'Zoth (an Old God that's been played up more than Yogg, mind you), then Azshara likely for the mid-tier. If Azshara as the final boss, likely N'Zoth as the mid-tier as seems to be traditional for Old Gods, with Azshara setting up for the Legion's return in the expansion after.  Another theory running around based on a tiny bit of lore in a WoW RPG book, which is very not canon, mind you, (  Quote:  The Dark Below is a place inhabited by demons, devils and infernal creatures, from where some sorcerers take their power directly and sometimes have a patron beast to foster their magic.  ) is that the expansion will feature a separate faction of demons not aligned with the Burning Legion, and their home realm of the "Dark Below".  