Last night at the L.A. premiere of Wonder Woman, Variety talked to producer Charles Roven and he shed some light on Joss Whedon's exact role behind the scenes of the Justice League and when he actually started. It was sooner than we all realized.
I think it's safe to assume the "additional photography" he as referring to would be a post-credits scene for the Justice League that sets up Whedon's Batgirl. Joss stepping in and filling a bigger role due Snyder's absence is a good thing for the Justice League.
Whedon may be able craft a bit of his superhero magic into the film and truly help the DCEU at large gain stronger footing in a genre, that some could rightfully argue has been dominated by Marvel. And seeing how Marvel's success is partially due to Joss Whedon, I think things could actually get brighter in the DCEU. "In Joss We Trust."