JLA doesn't need a "qb" to fomr the team, it can easily be anyone or just by chance. Keep in mind, the original Avengers were not formed by Nick Fury. They just got together to battle and joined up and formed the group afterwards. To be honest, a worlds finest movie would more plausible at this point and could just be as epic as the Avengers. If I were DC/WB, I'd tackle that first before venturing to a JLA movie.
When I say qb I mean both someone to be the face of it like RDJ and ways to show all the films are connected like a Nick Fury or Agent Coulson.
World's Finest could be really interesting...instead of a full Batman reboot, they could do a soft reboot like Incredible Hulk and jump into that story.
It's just looking down the line...you got a Zach Snyder movie, a sequel to something everyone hated, a reboot no one wants and chick action movie they've been failing at making for over a decade being your lead-off movies...that's rough.