Of course they are! What did you think they'd be hard at work on? A new restaurant modeled after Tartarus?
Speaking with Famitsu (and translated by Andriasang), Atlus executive Katsura Hashino says that the team has submitted work and begun development of Persona 5. That's right, a numbered sequel! Will it be here on the PS3 and Xbox 360 or is Persona 5 aiming for release on next-generation consoles?
But that's not all! Hashino also says another collaborative project is in the works, but the announcement is still far out. Wild speculation! That's what comments are for.