GOMU-GOMU no Mi Awakening is one thing we cling on as our hope to see Luffy develop a bit. Probably Vegapunk might help him. This man been mentioned since 2007 and it's been a DECADE. The more Oda delays his appearance, the more bigger it gets around this man.Seems he's reached ceiling of his devil fruit power he's mastered his haki abilities. I think at this point for him to be stronger he'll need a new devil fruit ability like black beard.
What is left for Luffy to do to get stronger.