3. Batman: Court of Owls
What better way to get Batman more aligned with the Justice League than by adapting easily the best opening storyline of the entire New 52 DC Universe reboot. Batman discovers evidence of an ancient illuminati-like group called the Court of Owls and finds himself at the mercy of its Talon a deadly assassin with greater prowess than even the Dark Knight himself. Its a web of intrigue which Batman very nearly succumbs to, and mixes high octane action with some awesome noir-style detective elements; which I still think were sorely missing from Nolans take.
How It Could Work: The actual story is disconnected from Nolans continuity, but it begins at a point by which we already know everything we need to know about Bruce Wayne and Batman. Bear in mind, this character needs little establishing by now, even to those whove only ever seen the movie adaptations. With that said, a Court of Owls movie could hit the ground running; we know who Batman is already, so theres only need for a reference to his origin (placing a rose in crime alley perhaps, to commemorate his parents death?) before diving right in to the investigation.
Potential Issues: I cant see many, really. The Court of Owls arc (which ended up us as a DC event thanks to its reception) was an extremely popular one that kicks started the New 52 with a bang. What better way than to ready a Justice League movie than to adapt one of the freshest adventures of the Dark Knight?