I think there's a slight chance that we will get one of these guys:
Stargirl
Mr. Miracle
Big Barda
Hawkman
Orion
Wildcat
Dr. Midnite
Sandman
Dr. Fate
I base this on that they're all featured in the 'Hall of Justice'-arena. Darkseid is in the map too and he got in, though I am aware of that he is the only one actually moving, the others being statues and costumes. Giganta and Atom Smasher is there as well (in the flesh) but their superpowers are not really suited for the game. I really cross my fingers on Sandman since word around town goes that he will be in the Justice League-movie. Might be nice for more to get to know him, he's a cool character from the more unknown part of DC Comics.