During an interview Willem DeFoe randomly disclosed how he fantasizes about the concept of portraying a "Joker" character in the Todd Phillips universe, likely as a rival or imitator riffing off of the original Joaquin Phoenix Joker and being a source of conflict in the movie.
Willem Dafoe "Fantasized About" Inserting Himself Into Joker 2
Willem Dafoe has an idea for a Joker sequel where he gets to play a version of the villain he never discussed until now.
boundingintocomics.com