I like the how this mini-set introduced Starcraft cards into Hearthstone.
How about a war of Angels against Demons?
For instance, some classes will side with Archangel Tyrael while others team up with the forces of Hell.
This would bring Diablo cards into Hearthstone.
You could have thematic decks. For instance, make Shaman into a Witch Doctor build, Death Knight will have a Necromancer deck, and Paladin will have a Crusader build.
This could be fun. What do you think, guys?