Here's the details. It's going to take place in Shibuya from Aug. 31 through Sept. 2nd, though the info here is for events on Sept. 1st and 2nd.
It sounds like some FFXIII-related news is on the horizon. Rumor has it that Versus XIII was cancelled, so maybe nothing related to that game
There's also going to be an FFXI music presentation and an update on FFXIV ver. 2.0.
The next day, a 15th Anniversary stage for FFVII will feature appearances by voice actors. There's also going to be a discussion about the future of FF in general.
That's all I've got. Start your speculation engines!