After the explosive finale to their Arkham trilogy, [Batman: Arkham Knight](tag:2683936), Rocksteady could make any game they wanted to (well, as long as DC lets them). Here's a couple of characters I think they could create great games out off.
Hear me out. His first game could be tied in with Arkham City, exploring what he was doing during that. I imagine he was doing more then carving pretty pictures into rooftops. His second game could tie in with Arkham Knight and his third game could see him directly take on the order of Saint Dumas (Unless you where one of the mean people who tried to kill Batman in Arkham Knight).
2) Red Hood
If you have the Red Hood dlc you know how much of a badass this guy is to play as. The game could take place after the events of Arkham Knight and explore what happened to Gotham once it lost the Batman. Players would get to further explore the fun of shooting bad guys in the head whilst still being a vigilante in Gotham.
Having played as Robin, I don't think his gameplay is very good so I'm not a fan of this idea but it's always a possibility. This too could be set after the events of Knight, although red hood would be a better way to go.
I think this would be great. Playing as Nightwing is always amazing. This could be set during Arkham Asylum but have it be in Bludhaven. Unfortunately Rocksteady might not go this way because they're not bringing anything new to the table.
5) (Please don't hate me but...) Suicide Squad
I'm not gonna spend too long on this one because I've got no idea how it will work. I just think that it will be fun too play as the worst of the worst all the way through the game not just in challenge maps.