Is this factual or just your guess? Because reading up on this they don’t seem to want to introduce Batman to this franchise and it also seems to be a different Joker than the ones that have made the film. I think he’s always gonna be a nut job and never some mastermind.
The Joker if you are familiar with comics, when he fell in the chemicals, he learned later that the makeup was permanently attached. That’s what made him totally insane.
That sub-plot has been with all Joker live action and animated content since the 1960s.
These Joker films are not in the DCEU, James Gunn DC or Robert Patterson (The Batman) films and are in their own universe.
The first film, the makeup he put on, from what we see in the trailer in this new film, He is still applying the makeup.
So it’s clear either the end of this film the makeup is permanent or the next film. I doubt we will see a new Batman introduced with them going at it, but the franchise will most likely end with them getting close to meeting up and we the audience pretty much knows what happens which will end the franchise.