While Gear Five is surely Luffy’s most powerful transformation in One Piece until now, the Straw Hat captain could keep evolving his powers, especially now that he needs to face the strongest villains he has ever encountered, the Five Elders. Recent developments in the story tease exactly how Luffy will evolve his Gear Five, and this could take inspiration from a Hindu epic that was already referenced once in One Piece.
https://screenrant.com/luffy-eat-mother-flame-one-piece-hanuman/