i think they could do penguin. tim burtons penguin was the only fucked up looking one. in the regular comics he was just a short fat guy with a long nose and liked the penguin bird. if they did do penguin i would expect it to be like a mob boss type of villian.
riddler would be cool villian if done right.
i dont think mr freeze could be done. that is too far out there (unless they do the original). so isnt killer croc, man bat, bane, and clay face.
who wants to see the scarface dummy and mad hatter? not me. i could say that about the scarecrow but they did him right.
poison ivy and catwomen i could care less about. harley quin isnt anything without the joker. i doubt they would hire someone else to do that role.
i hope there is no robin or batgirl (who is commisioner gordans daughter).