It's emerged in Japan today that Square Enix are planning to release a brand new Final Fantasy experience on the Nintendo 3DS called Theatrhythm: Final Fantasy.
As the name of the game suggests, it will be a Final Fantasy title based around theatrical action. In other words, it'll be a Final Fantasy music/rhythm game.
Aside from the rhythmical battle system, it's said that the game will share many other traditional elements, such as towns and dungeons. No release date has been mentioned this far.
Source: Final Fantasy Union