I LOVE this idea and would be all over it! I've got a journal for Tagg from The Taggerung and I've often thought about how much fun it would be to AU my Viking warrior as a very angry wolverine. I will say you're going to have a niche audience for this sort of thing, and the last time I was in a completely AU faction game about seven years ago, what caused it to die is that there just weren't enough people to sustain the different factions. So maybe also consider ways to keep the game going if you've only got, say, ten players.