Kate Kane (Batwoman)
While Rebirth has a major hard-on for Kate Kane right now, introducing Batwoman in The Batman would be a really bad idea. Not only would it detract from the titular hero, but it would also ruin the spotlight for Batgirl. Remember, folks, not many people know the difference between Batgirl and Batwoman, so there’s no need to muddy it in the DCEU.
You see, Batwoman is a character that you would introduce in phase three of a franchise. This is the stage when everyone has already been established and you can start bringing in the names that aren’t widely known to the average person. By this time, the audience will be more receptive to new heroes and actually want newer characters as well.
Kate’s a legitimate badass and her time on the screen will come, but now’s not the right opportunity. Let the universe be built first; otherwise, it’ll be like chucking every character at the audience and hoping they’ll stick.