Guess Oda is coming closer now to show the link between Joyboy(and his successor Luffy) in the ancient kingdom, the ancient weapons future role against the alliance of nation(20 kingdoms later known as World Government)
And judging by Vegapunks wording here
It's likely many of these islands were connected to one another
And infact we already saw a hint of it with the existence of ancient Wano residing deep undersea
The connection between Joyboy(and his successor Luffy) and fishmen island, Shirahoshi's day of birth(ancient weapon capable to control neptunians), the existence of Pluton in Wano, Vivi(likely Lily's descendant - viewed as traitor by the Alliance of nation), the Ds against Celestial Dragons
Every pieces are slowly but surely coming together