The official Mistwalker site has been updated with what should be the first artwork of Sakaguchi's next big RPG project. Nothing much is known about the game except it's supposed to be Sakaguchi's most complex project ever. The artwork itself is by Kimihiko Fujisaka, who worked on Drakenguard before. Of course, no platform has been announced for the moment.
Edit: Fujisaka says the artwork is not of Mistwalker's next game, even though he's working on it.