The idea of Leia as a villain is just too silly for me to take seriously. So I'll say no to that one.
I'm hoping the villain isn't a Sith. I posted my thoughts on this a long time ago, though I don't think it was in this thread. Assuming there's a Jedi Academy, I'd like the villain to be a rogue Jedi of sorts who teams up with some other bad dude and they do only vaguely bad things. Let's have some shades of gray (not fifty though).