I agree with everyone praising the Animal Man and Swamp Thing comics, they're incredible.
Obviously I want Swamp Thing and Animal Man in, but lately I've been thinking that all 3 will be in.
What I'm thinking is that Swamp Thing and Animal Man are both critically loved and popular new series, not to mention they'd offer variety in terms of gameplay, so one they stand a pretty good chance. In the story, Animal Man could be convinced to join Superman (he's all about justice) and Swamp Thing could be convinced to join against the regime if they're building prisons on forests or whatever. I don't know how they'd be integrated exactly, but I think (and hope) their chances are high.
Now Batwing is a totally new character and I find it almost impossible that DC wouldn't jump on this game to market a new character. Batwing is the only one to get his own spin off after Batman Incorporated, DC obviously has plans for him. Story wise, we can assume that the main villain will be Ares which would make this a global conflict. In the New 52 Ares is stationed where the war at, in Africa. Batwing could get his scent and holler at Batman warning him of this. His role in the story would be going to check it out, fighting villain after villain and then getting killed by Ares and setting the second-act in motion