Speaking as someone who's been itching to play villains doing bad things: If players can app characters to play on the evil side, why not just let them app villains instead of nebulous "AU characters"? I don't care whether or not AUs are allowed, I've been in games that did the "there can be one OU and one AU of each character" and it was fine, but splitting it up by OU = good and AU = bad seems silly.