I think beastmen could be an interesting faction. Just lump all the mythical monsters together sort of like in Narnia.
-Minotaurs -Saytrs -Centaurs -Harpies -Gorgons and maybe throw in some of the modern fantasy guys too. -Gnolls -Kobolds (The dog/humanoid kind)
Lizardmen should certainly be grouped with dragons.
Steampunk dwarves have been done to death. I'd rather see the faction focused on other things. Goat mounted cavalry? Animated ancestor statues? Giving them a gnome unit might be cool.
I think a barbarian faction has a lot of potential. Sort of a mash up of Vikings Huns and Conan. It might be hard to make them distinct from orcs.