I am only okay with them throwing joker in the sequel if they go the Thanos route with him where he just sort of shows up and then disappears again like "....soon I'll do something. soon. one day." and then we don't see him the rest of the movie
We got riddler and penguin, I think that's second movie for both. Hopefully we can do at least some of the others a first or second time before we circle back to the clown prince of crime