Hironobu Sakaguchi has a conference scheduled for July 2nd at the Japan Expo in Paris. In the conference description it says...
He will also present his latest project, which is kept secret for the time being
So that's something to look out for if you care about what he's up to next. His latest game was The Last Story with Mistwalker and I'm not sure if this next project will also be handled by the same company. Either way, I wonder if this'll just be some concept art or if he'll show something solid.
Also Persona 5 news in July you heard it here first
Update: "Terra Battle" has been trademarked by Mistwalker, so it's likely this project that Sakaguchi will be talking about.