I still say Azrael or Bane, or both. They're the only foes that would 1)fit in with Nolan's take on Batman in general and 2)have enough conceptual strength to carry a film.
Azrael would make an interesting antagonist for a Batman film. A fairly straightforward adaptation of Sword of Azrael
would work within the context of Nolan's work. (It would also be an ersatz James Bond film.)
Azrael as an opponent manipulated by Talia into taking on Batman, though, would be downright fantastic.