Jinbe, like Brook, is one of the older members of the crew. There is a lot of his life we know little about.
Specifically, I think there’s one core fact about Fishman Island that I think could open the door for a second Jinbe flashback.
That being that it is one of the few places we can be certain that the burn scar man visited. After all, the missing road poneglyph, the one the burn scar man has, was once located in Fishman island.
Ultimately, like Oda is coupling Brook and Gunko’s past, I think he could similarly couple Jinbe and the burn scar man’s.