One of the things I've admired about Affleck is that he isn't rushing The Batman at all. We know practically nothing about it except that Joe Manganiello will be playing the villain, Deathstroke. And speaking with The New York Times [via Batman-on-Film], Affleck explains his measured approach to the film, also revealing he and Geoff Johns are still writing the script...
“We still have to get a screenplay and get it together. I’m a real believer in not reverse engineering projects to meet a window or a date, but rather when you get the right story, the right idea, the right thing, then you make the movie. That’s what we’re doing, and I’m hoping to get that done. I’m spending a lot of time working on that, but also working on other stuff.”
“If I could, there’s nothing I’d love more than to direct a stand-alone iconic, great Batman movie. But it’s been done. Chris Nolan did three really great movies. I’m really mindful of that. I’m not in any hurry to jam the mediocre movie down the pipe. I really want to make sure, if we do it, we get the great version and one that’s worthy of tradition of guys like Tim Burton, Chris Nolan, and Christian Bale.”
He's got the right idea, I think. Get the story right first and worry about timetables later. That said, Warner Bros. may not be keen on that approach. They have an entire franchise of movies to worry about.