Oh, ta.
I've got a few ideas running through my head, but I don't know how easy or popular they'd be. Ogre mercs based on different cultures, countries or smaller regions. Non-goat beastmen. Alternate Cold Ones. But I've been reading the recent
nooby questions thread in the Warhammer Background board, with all it's discussion about how magic works (or doesn't work) in the Warhammer World.
So right now, I'd like to see takes on old world wizards at some point on the gradual path to corruption. That is, not a full-blown Chaos sorceror with two-foot horns and a big icon of Tzeentch on his back, or a necromancer with a serious bat motif!
Although mutation could certainly play a part. I can see a lot of possible variety, including that. College wizard or hedge wizard? Mixed the winds of magic wrongly; exposed to warpstone; read the wrong book; ensared by a cult? Horrified or pleased by the realisation? Trying to hold it back in some way, maybe while still taking part in whatever caused it? Little mutations like a patch of scaly skin, or big 'uns like limbs replaced with tentacles? Or no mutation - just slowly and steadily going off their nut?