If they bring riddler, i say hugo weaving
He has shown in v for vendetta he has the proper voice and speaking speeds to be able to ramble off riddles and sentences to no end, that movie plus matrix shows he can pull off action scenes
If they WOULD bring in robin, they could do an awesome bane\similar to knightfall storyline.
They dont even really need to establish other main villians. Just have bane break people out of arkham(similar to batman begins) and have batman fighting constantly to bring them back. Just have a bunch of psychopaths and murderers.(i recall one from knightfall, a murderer who cut himself for every person he killed)
With fox, you can make him into azrael\cyber suit batman if you want to have bane break batman.
As for who'd play bane, for a sec i thought they were retconning and gonna make tiny lister(zeus\prisoner who threw out the detonator) as the future bane since it was odd how they made him a minor char of importance.