I think a certain Andrew Garfield may be swinging his way around Manhatten at the time!... but having read up on Batman's list of adversaries (not having read the Comics), Black Mask really would make for an awesome and fitting villain, given where the story is atm.
Tom Hardy is awesome, by far one of the best british actors around atm.
Killer Croc is being rumoured on the internet, but surely there's no way they'd dare venture down the CGI villian route!... it all but ruined Spiderman, and Nolan hasn't felt the need to use it yet and all for the better!
Unless they very much alter the character and have him as a human character and Killer Croc only by name...
Just leave out the reptilian part!
And can you really look past JGL as the Riddler atm, unless that goes to Tom Hardy, which could work just as well!