I thought they were making the Batman game with Damien Wayne (ugh, Damien... why him?), but that's from the creators of Arkham: Origins, so who knows?
Despite the problems with Arkham Knight, it was still an incredible solid game. True, way too much Batmobile, but I thought it played very well. Gameplay was as good as ever, and I don't think anyone does the "Arkham fighting-mechanics" as well as they do.
Putting them on another Batman game would be silly, but I would not be opposed to see them do another game based on a different DC-character. Maybe the Flash or Superman? For something really out there, I think making a Green Lantern game would just be perfect. Creating your own constructs, going to space, fight with other lanterns.