Rocksteady has proven themselves well at making a single character driven game. I don't think a colourful cast like the Suicide Squad would translate as well. Firstly, multiple characters always seem to make a game less enjoyable. I mean while I like playing as Catwoman, Robin, Nightwing etc in Arkham City, they just feel like watered down versions of Batman. Deathstroke was really no different in Arkham Origins either. I'm interested to see if this improves with Harley and Red Hood for the upcoming Arkham Knight. Should it actually improve then perhaps I could get behind a Suicide Squad game but as it stands I can't really think of a game with multiple player characters that has been well done. Honestly the Lego Games and Donkey Kong 64 are the only things that jump out in my head (The Lego games have been some of the most faithful adaptations in years compared to other Superhero games out there). Fighting games have large varied casts and generally are alright, Injustice Gods Among Us was a great fighter game with DC Characters. Rather well done if not a little odd in the art department (Seriously what was up with Harley's default costume?), but I mean it was a fighting game. The story was weak and contrived (I'm surprised the comics are still going, should I be expecting a sequel game soon then?) but it was comic book worthy I suppose. 

I would like to see Rocksteady tackle other heroes and do for them what they've done for Batman before running off to do a Suicide Squad movie. Honestly though, the Arkham games owe quite a bit of their success to Paul Dini and his involvement and influences especially the numerous connections to what is arguable the best best Batman series ever... Batman The Animated Series. On that note, I think once Rocksteady is done with Batman they should take a crack at Superman or maybe stay in the same vein and try Green Arrow out. Alternately I could see a game based on Flash being fun but Green Arrow seems like he would be rather at home in an Arkham styled game. 

They could finally make 'Green Arrow: Escape From the Supermax' a reality. though likely a better title and probably go with the grittier and now more familiar 'Arrow' name instead of 'Green Arrow'.