honestly this might be a stretch but i was thinking. maybe they could make jinchuriki status similar to the Kage experience, there’s about 9 jinchuriki and every 6 months (just a time period i’m saying based on kage it doesn’t matter too much) they switch out. that way it gives jinchuriki a long enough time to have fun with it but also gives other people a chance every so often.
oh in that case i change my vote to the Sage Mode, Curse Mark, etc.
i think with that should also possibly come a system for the Hiden Techniques rory spoke of a long time ago with Raijin Teleportation, Rasengan, those type of things that don’t belong to an Element but still should have a place in the game.