Ok so Joker definitely needs to be in the GCS movie but I'm not sure if Leto would want to be another tangential, superficial role in a story as the Joker. I think he wants to be front and center from here on out. here's my suggestion: they can get around that by re-purposing the footage that was left on the cutting room floor for SS. he did say they had enough stuff for an entire joker movie. We definitely know they cut scenes with Harley being joker's therapist, them kissing (when he asks for a machine gun) and that whole arkham scene in general. They cut out a lot of scenes to make Harley and Joker's relationship go from clear-cut abusive, to co-dependant and messed up but still loving so I think they probably have a scene where Harley and Joker have a falling out. That could make it so we can have the Joker in the movie without needing to make Jared play a fringe, subsidiary role/annoy him even more. It would be a win-win in the sense that it could put that footage to good use, show it to audiences who never got a chance to see it, make it serve a purpose story-wise, flesh out those scenes we only saw small snippets of and maybe even appease Leto who was salty that his work never saw the light of day. kind of like a peace offering of sorts. I'd personally really like to see those scenes fleshed out. It would kind of feel like when they re-visited the Battle of metropolis in BVS. familiar but new and interesting. I'd love it if GCS started off with the extended Harley and Joker Arkham sequence. Would be an awesome opening to the movie. who knows? maybe the whole reason they held back from putting those scenes in the ultimate cut was because they planned to use the footage like I'm suggesting.