Glamour magazine lists their casting choices, and first is
Kristen Stewart
http://www.glamour.com/story/batgirl-movie-details
I note this because I've advocated for Stewart on the Barbara Gordon casting thread for 'The Batman' (she's a terrific actress, looks right for Babs, and has often independently repped Batman, wearing Bat t-shirts in public, which is awesome), and because none of my choices for a comic book movie role has ever made a media outlet list anywhere, ever (so, hurray for me, I guess).
Anyway, the writer also states "this is never going to happen. She's way too cool for a superhero movie, which is exactly why she's perfect!"
But hey, I never really thought a Batgirl movie could happen, so, who knows?