It's unlinkely that they'll do FFXII. The game had no "main character", so it'd be hard to pick a protagonist without making fanboys rage. Same with the antagonist, there really wasn't one. Gabranth did his duty, and Vayne wanted to free humanity. FFXII wouldn't work beings that Dissidia seems to be have very strong themes of Good vs Evil. FFXII's morally grey characters would not work in that context.