Affleck previously mentioned he was working on a project with Johns, and it was also recently confirmed Affleck wrote a Batman script.
Here's what Kevin Smith had to say about Geoff Johns working on Batman:
[Ben Affleck's] been working on a [Batman] solo script with Geoff Johns as well. Last conversation I had with Geoff Johns, I was like, "Are you working on it?" And he said, "Yeah." I said, "What's it like, man? How do you co-write with someone?" And he's going, "We just break it up. He takes halves, and I take halves and then we write, and then we switch material, and then he goes over mine, and I go over his." That sounds so f---ing fun man.
Smith also previously let it be known the Batman script will be better than the Batman Vs. Superman script.
It's been said Ben Affleck hasn't signed on yet for the Batman movie, but WB just announced release dates for two new DC movies, with one of them more than likely for the new Batman film.
So it seems we're just waiting on the official announcement from WB about Batman. Maybe at this Summer's Comic-Con?