ok. long shot theory here. I will try my best to explain these ideas systematically, but these are EXTREMELY abstract:
lately, i, and other people within the One Piece fan community, have been suspicious that Luffy is going to go back in time. \* Especially after Oden's reference to a particular hero traveling "800 years" to the present. Which is Oden's ultimate motive for guaranteeing that Wano's borders are open 20 years after his passing. \* Most important to note, is that I'm not convinced that Luffy has the strength to overcome the likes of Kaido, Big Mom, the Admirals, and ofc, Blackbeard. Nor is it very believable that Luffy could acquire such power by the end of the Wano arc. (I am also very aware of the convincing theory that One Piece is centered around the consistent theme dubbed "inherited wills." which is holds a lot of water...)
Now, this is where it becomes difficult to describe, or even substantiate, a "time-travel" theory. So bear with me. First, I believe that Law is going to die in Wano... But not before using the Ope Ope No Mi to grant Luffy ( but I would love if it was Usop lol) immortality... in an act of sacrifice. Strategically of course, so that Luffy can survive being sent back in time... to survive the 800-year journey back to the present. \* granted. I have NO clue whatsoever how traveling back in time is remotely possible. But given the abilities of Kozuki Toki to travel forward in time; I am optimistic that it's possible... 3. Upon going back in time, Luffy will be in Wano, 800 years ago (roughly). This would develop the relationship between "Joy Boy" and the ancient Kozuki Clan. Insinuating that Luffy IS Joyboy ???? *\* ALRIGHT. I am also aware that the massive straw hat seen at the summit of the kings was far too large to be luffy's. Yet I am not convinced that this is a complete contradiction to the theory.
***How awesome would it be, that Luffy is alone in the ultimate quest to make it back to the very moment he is sent back in time, as a FAR more powerful version of himself, to be with his crew???!!!