Following WB's next animated movie, Justice League: The Flashpoint Paradox, it appears as if "Justice League: War" is the title for the next film.
Appearing on the box art for Flashpoint, it's stated that included is a sneak peek at "Justice League: War."
WB has been including previews to their upcoming new animated movies on their latest releases, so this looks like a confirmation on the next WB animated movie.
Justice League: The Flashpoint Paradox, a PG-13 rated film, arrives July 30, 2013 from Warner Bros. Home Entertainment on Blu-Ray™ Combo Pack ($24.98 SRP), DVD ($19.98SRP) and Digital Download. The Blu-ray™ Combo Pack will include UltraViolet.