It seems as if the overarching theme, and by extension, the gameplay, would involve the concept of "agency", according to an interview with Persona 5's director, Katsura Hashino, as reported by Design & Trend. 

In an exclusive interview with Game Informer released on December 9, 2015, Katsura talks about the game, the characters and the gameplay, but reveals details such as the concept of agency being central to the plot, and the concept would also influence the gameplay as a result. "We think that sense of agency is one of the charms (...) one of the aspects we're most excited to bring to you."

He also explains that the characters of this installment will voluntarily take the role of "phantom thieves" and will actively run into the thick of things, so to speak, instead of being dragged into a mess and trying to solve things because they have no choice. The characters' actions due to this will "draw the attention of an even greater enemy... That's how the game sets in motion."

The gameplay of Persona 5 will add new features to the staples of the series, and some will apparently modify some of the iconic features of the series. Some of the changes, as listed by Master Herald, are as follows: Social Links will presumably be replaced by Cooperation, but is said to function similarly enough. All-Out Attacks that now look a bit more brutal than the previous installments as well, and the recent trailer even hints the return of Demons, who have not appeared since Persona 2. It also seems as if the game has some minor platforming capabilities, a navigational app to let you sneak into the Palace, which is the alternate world the protagonists will be able to explore, the ability to steal masks from Shadows which you can equip as Personas, the ability to sneak around obstacles and enemies, and players will also be able to hearts of the "wicked", and that would be the main objective of the game.

Persona is set to be released on the summer of 2016, and will be available to play on PS3 and PS4.