After thinking about it, I dont think the last scene has anything to do with Luffy's Devil Fruit.
This is specifically the hat itself melting. However, Oda will probably tie it somehow to DF awakening...
Even tho DF has nothing to do with Joyboy or maybe it does...
The hat itself could be Joyboy's, passed down from generation to generation.
If the hat has inherited will of Joyboy inside of it, not sure why that would affect Luffy's Devil Fruit...
This is specifically the hat itself melting. However, Oda will probably tie it somehow to DF awakening...
Even tho DF has nothing to do with Joyboy or maybe it does...
The hat itself could be Joyboy's, passed down from generation to generation.
If the hat has inherited will of Joyboy inside of it, not sure why that would affect Luffy's Devil Fruit...