I think the One Piece might be hidden in a sunken island.I can't help but remember about Enies Lobbies when the spoilers mention the hole where Lulusia Kingdom used to be.I think the same thing happened in the void century and some island were sunk thnx to the rising water level.
I can see that happening definitely. We might get a proper Atlantis with the possibly sunken Ancient Kingdom or even God's Valley, which could explain why it disappeared too, especially if it was where Enies Lobby is now too.
I do think the SHs will go to space but also ocean floor/underwater again in future. Robin mentioned Davy Jones at Long ring Long Island IIRC and Davy was mentored again at Fishman Island? Hody might be related? Lmao.
Maybe Hody was reincarnated by Davys hate of when he was alive, like theories of Imu being the personified wrath of the sea as the apparent curse about devil fruits relates to too?
Although that mysterious whirlpool guy could be Davy for all we know. I hope it's him, a Rocks or at least Roger pirates or even Dragon with a wind/weather or vortex fruit causing those whirlpools lol.