I'm still looking forward to Dogs of War units that can be for both order and Destruction use. Ogre Kingdoms units which I think they can do something really interesting with. Tomb King army would be a really neat theme. I would love to have a giant bone scorpion unit. the Brettonions have only been hinted at. And said by others...all of the books available with material. Not to mention there are still plenty of units and spells that have not been put in to play for all of the original armies. This game still has quite a bit of life lef in it. It's just getting started really.

With any theme I think they would run out of main characters soon, be it Star Wars, Cuthulu, LOTR or whatever. But there is still plenty to draw from other material and "extrapolating" some of the units and concepts. Also, the limitations via the original theme and novels really only affects units and legends and to a much lesser degree support, tactics and quests which can be developed infinitely I guess.