The assumption here is that there will be a season 3, and, like Greg Weisman said, there will be another time skip.
Personally, I'd love to see Stephanie Brown as Batgirl. I know the chances of that happening are slim to none, but what the heck, she's an awesome character and the Batgirl persona just made her better.
Supergirl would also be a great addition, I think. And maybe Ravager.
EDIT: I haven't been following the new 52 at all. Could someone tell me if Steph is still a part of the DC Universe? And if she is, how much of her history is still canon?