Bandai Namco Entertainment and Omega Force have announced that One Piece: Pirate Warriors 4 is in developement and is set for release sometime next year.
The news was revealed at the Anime Expo 2019, where Digimon Story Cyber Sleuth: Complete Edition was also announced.
We have a trailer (which you can watch above) to get a feel for what to expect from the game but other than that, news is sparse. However, the One Piece: Pirate Warriors 4 "will cover many of the stories and arcs from One Piece," according to Dualshockers, rather than tell an original story.
One Piece: Pirate Warriors 4 is set for release in 2020.