It's too early to tell; however, this patent application lists Tetsuya Nomura as the inventor of a character switching battle system for RPG/action RPG games. The system allows players to control and switch to temporary characters during combat — meaning, you can hop in the skin of another character. When time runs out, players then automatically change back to their main character and inherit the temp character's abilities.
The patent does not specify a platform, stating the combat system is designed for "a portable gaming apparatus." The apparatus included in the patent looks somewhat like the PSP.
More details in the link below.
Is This One Of Tetsuya Nomura's Unannounced Games? [Siliconera]