For a while now, it's been common knowledge that Atlus is making Persona 5. In a recent interview on Famitsu.com, Atlus game designer Katsura Hashino briefly (and I mean briefly) mentioned the next, numbered Persona.
When asked about the latest in the Persona series, Hashino replied, "We're making progress on developing the next numbered Persona."
That, of course, would seem to be Persona 5.
After being asked for more details, Hashino said, "We're not at the same where we can talk, but when the time comes, we'll reveal details, so please wait for that."
Back in 2010, Hashino told Dengeki PlayStation they were "preparing to start work" on the next Persona. "I want to add things that are being expected of the series," Hashino said. "I also want to change things that can be changed within those boundaries."