http://comicbook.com/dc/2017/04/18/b...dios-avengers/As revealed to The Hollywood Reporter, Feige said that Whedon actually contacted him before the decision was made public.
"He called. A couple months ago, which he didn't have to do and was super cool of him and super nice of him… And we couldn't be more supportive. We want to see a Joss Whedon Batgirl film be awesome."
This hints toward Batgirl being in the cooker for more than a few months now before it was announced so we might be getting a Batgirl movie news sooner than expected. By San Diego Comic Con this movie could have at least 6 months of planning with scripts etc by then. Also this is all just me theorising.... I saw a lot of people saying it's going to be on the slow burn to make way for Nightwing and Gotham City Sirens, but with Joss he has a solid amount of quality work and more experience behind him than the other directors (not to diminish their accomplishments but Joss helmed two Avengers movies with Marvel execs breathing down his shoulder so I give him the edge on that).
So yeah, because of Joss's experience I wouldn't be surprised to see this movie move at a faster pace just because he's knows the ins and outs. I also theorise that this might be a passion project or a character that DC let him choose to do a movie on (because in the grand scheme of things Barbara is sort of random character to get her own movie straight away) so he might be able to translate his vision easier than others. Also it's a solo hero project and WB would definitely let a guy with the success that Joss has to do his own thing.
I'm not saying the movie is getting fast tracked at all, but a Batgirl movie with the creative force behind that it has might make things move quicker along