The Batman director Matt Reeves recently made waves by saying that the film won't be a part of DC's extended universe. This comes hot on the heels of the reveal that Todd Philips is working on a Joker origin movie, that won't be a part of the DCEU either. In an interview with KCRW, Reeves said that he was approached by Warner Bros about making a "standalone" movie that is "not part of the extended universe." It wasn't until the Philips news broke, that the pieces of Reeves' statement were put together.
If this is true, it would make sense that Ben Affleck would step down from directorial duties and Reeves would ditch Affleck's original script, in order to separate the movie from the rest of the DCEU.
It's only a matter of time before Martin Scorsese is announced to produce The Batman like he's doing with the Joker origin film.