Geoff Johns is a well of DC knowledge and lore within DC Comics, and he brings that same expertise to Warner Bros. and their big budget superhero film Batman V Superman: Dawn of Justice.
In an interview with DC All Access, Batman actor Ben Affleck spoke a bit about working with the popular writer during filming, and that they have something in development outside of just Batman V Superman.
"Geoff Johns is a brilliant guy. I consider him to be the most valued resource on all things comic book, and every time I like something in the comic I always mention it he's like oh yeah I wrote that. Now I just think he's bulls******* me and he says he wrote everything. You know he and I are working together on something and I really am excited about it, and I love him, he's the best."
While we don't know if it is in regards to a film or possibly something involving the comics, anytime Geoff Johns is involved it's probably something worthwhile. Hopefully we'll hear more about the mystery project soon.