I think Nolan could definately change Bane into a believable character, but I just don't think he would want to spend that much time and piss off fanboys at the same time for changing the character too much. But I must admit the "Batman's back is broken" line would definatley spark interest in just about any casual observer. And no, you aren't spoiling anything there. If anybody really cared enough about that story to be spoiler-free, they should have read it by now. I say one year limit on Spoilers, but that is just a personal opinon. You do know Darth Vader is Luke's father right?
I think you are right about the Riddler. He and the Joker are actually quite similar. Just replace Riddles with Jokes only funny to the Joker.
To be honest. I've never been a Catwoman fan. Plus Nolan would have to work even harder on her than Bane for audiences to accept her again after what Berry did.