Shame he's said no Penguin. Burton's idea, of Penguin taking over the city through politics, would work fantastically in the Nolan-verse, but thankfully, it is an idea that can transcend onto a lot of other villains (and a lot of villain's origins...) and my money is on something like that as a plot, it just seems to follow on naturally from the last two.
In Begins, city was corrupt, cops on the take, Mob running pretty much everything, Batman stood up to them, allies with Gordon and the DAs office starts to take notice.
Dark Knight, Harvey Dent tries to clean up the city, Mob takes two massive blows thanks to the Joker and Batman, vastly reducing their power and influence, Gordon made commissioner after old one murdered, but the level of corruption within police comes to light, film ends with Gordon and Batman struggling to save the name of Harvey Dent to give the city hope, covering up what actually happened to him in order to save face (pun intended).
So, Gotham is left with its vigilante branded the murderer of Dent, both its law office infrastructure and its organised crime infrastructure in tatters. Perfect fodder for a few new players to come in and build up their own empire (Croc from 'The Joker' perfect example, Hush, Zasz, Bane (can imagine being re-imagined as a burly guy on a steroid addiction rather than 'green goo o' doom'), Black Mask, pretty much everyone mentioned already.
As for Catwoman and Harley, I'd love to see both. Poison Ivy I love, mainly from the Animated Series, but from the movies less so, and I don't think she should be done as plant-like as she was in Arkham Asylum (though she was cool) but would be happy to see her done intelligently.
Catwoman I'd like to see given to someone Bale's age, and not a big name. Casting my mind over the casts of various Sci-fi programmes like Farscape, SG1 and Star Trek, can think of a few likely candidates that would fit the strong female character archetype without having to resort to cheeseball sexuality (and I'd like to see a Catwoman who was Master Thief first, sex-object second please, thank you very much Mister Nolan). If we get Catwoman, I'd like there to be the ambiguity as to her allegiance and alignment, and I'd also like to see her as a foil for a female bad guy such as Quinn. No need for cheesy back-story (Nolan has avoided them all adroitly so far, Joker being the best example) just have Catwoman show up doing what she should do, taking shiny things from difficult places without asking, the whole city in disarray backdrop perfect for some opportune burglary, especially with the Police force likely distracted searching for Batman.
Shame no Riddler... I was hoping for a revelation there.
Ah well, we'll have to wait and see.