Amazon Japan has listed Warriors Orochi 4 Ultimate for PlayStation 4.
While the listing has since been removed, the product description mentioned new playable character Gaia and the return of earlier playable characters such as Joan of Arc (who was last playable in Warriors Orochi 3). It also mentioned other additions including a new story, new side scenarios, new modes, and new actions.
An official announcement is planned for August 29. While the Amazon Japan listing was only for the PlayStation 4 version, like the original Warriors Orochi 4 before it, Warriors Orochi 4 Ultimate is likely due out for Xbox One, Switch, and PC as well.
Thanks, @Renka_schedule.