I think Weevil is the man with the burn scar.
Miss Buckin claiming that Vegapunk could prove Weevil's kinship to Whitebeard adds support to the theory he is a failed Whitebeard clone.
She herself was successfully cloned by MADS which she was part of. And was a Rocks Pirate meaning she had access to Whitbeard's bloodline elements.
If Weevil is a clone of Whitebeard he could have his memories which would be significant.
The last road ponelgyph was originally located on Fish-Man Island.
Which was previously under the protection of Whitbeard who Roger revealed some of the secrets of the world to. I think it's very possible he knew the last road ponelgyph was there meaning Weevil could too.
Since Weevil was captured by Greenbull there is a theory he will get a glow up.
Which would be a cool callback to this scene. But I think Weevil is a character that was already introduced.
I think Weevil is Kadar a rear admiral that fought the Sun Pirates. I think there is a mystery around since his ship was sunk even though Fisher Tiger promised to let him go.
Shiryu speculates that the man with the burn scar is a government man. Laffitte that he is a power user, since he rides in an all-black ship that swallows enemy ships in gigantic vortex if they wander to close. Kadar is a marine and his ship was sunk.
I think Kizaru is another hint, he took the reports for Kadar and Weevil which I think links the two.
Again I don't think the Sun Pirates sunk Kadar's ship. Fisher Tiger berated Arlong and JInbe for going too far. Arlong said he only killed one or two people.
I think Weevil ate the Hito Hito no Mi, Model: Umibozu. The umibozu is a yokai that takes the form of a monk that sinks ships. The umibozu was mentioned a few times.
Similar to Onyudo (Wadatsumi's epithet was Onyudo) before it appeared as a human zoan fruit.
I think Weevil awakened and his zoan powers consumed his mind which is why he is simple minded like the Jailer Beasts.
It think Weevil will regain mind utilizing powerful haki.
If my theory is true I think Weevil got disillusioned with the marines like Diez Barrels, went awol and sunk his own ship.
I think he Awakened in Wano. His neck scar looks like it could have been inflicted by Queen's collar. Apparently body parts can be reattached in Wano and Weevil's arm looks reattached.
I think Kaido tried to recruit him to army so sent him to the Prisoner Mine to break his spirit but he escaped.
I think Weevil's burn scar will be on his back where Whitebeard had his Jolly Roger tattooed.