Why in the world would they do it that way? Batman is the only superhero who's been consistently viable as a live-action film property for Warner Bros. in the past 30 years. I can see them using him, Superman, or both as anchors for other superheroes' films, similarly to Nick Fury's role in Marvel, but there's no way they'd put a moratorium on Batman solo films. He's their cash cow, uh, bat.
7 Batfilms in the last quarter century...they're just coming off a successful Bat-franchise that casts a large shadow....They'd be best to give him a rest when it comes to solo films. And giving us a new Batman who only appears in team films could generate more interest for those films in which he appears. He's been successful enough solo recently that they could afford to focus his efforts on helping the greater franchise rather than his own series.