Bring in Harley Quinn and have her be just as insane.
It's time a Batman film had a complete homicidal female role.
Catwoman is too "gray" of a character to have her be a "big bad"
I'd love to see Harley Quinn in a Nolan film - and she'd be more believable than Catwoman. It would also show that while Batman is still workin' alone, without even Gordan and the police on his side, the Joker is "inspirin'" others to follow his example in Gotham.