Assuming that important DC people check these forums…
Any Batman cameos and supporting roles for upcoming Suicide Squad, Pirds of Prey, or potential Nightwing or Batgirl films, keep the Batfleck. Let Reeves and Joachin Phoenix do their Earth-69 Batman and Joker things. If they are popular and the actors are down for the long haul, bring them in via a Crisis or Flashpoint thing.
I’ve always wished Michael Keaton would come back as Thomas Wayne in a flashpoint style movie. I know, it’ll never happen, but what a way to appeal to a large audience - young and mature. Right?
I do not want them to be done with Ben. He has solidified himself in the new DCU movies. They can’t just be done with him. I would be fine with him being left out of The Batman. But not the series.
Ben Affleck wanted to be Batman. You can’t say he didn’t. He repeatedly said it was f-ing amazing to be Batman, f-ing incredible to be Batman, it’s the coolest part in any universe, and so on. Affleck had already written a Batman vs Deathstroke story that DC animation director Jay Oliva called the best Batman script he’d ever read. Affleck was ready to direct. Whatever happened behind the scenes, I can bet it’s not Affleck who simply wanted to quit. It was WB that forced him out.
I like the OP’s idea a lot. Ben, despite my initial misgivings, turned out to be pretty damn good for that Batman, and if we are lucky enough (probably not as WB sucks at this) to get more films in the Snyderverse that feature bats, or the League (release the damn Snyder cut!), Ben should absolutely be a part of them.