They have been sticking with the non-superpowered villians in this latest run of movies. I really don't see any of the iconic SUPER-villians coming out like Poison Ivy, Mr. Freeze, Clayface, etc. I'm betting they are going to stick with one of the major crime syndicate boss type badguys and maybe throw in somebody like Deadshot.
The Penguin is always a good option, so long as he's not an ACTUAL penguin this time. Just a mob boss in a tux, maybe have him hire Deadshot (another somewhat realistic villain) to take out Batman?