I honestly don’t understand how there isn’t some kind of Waterworld… either action/fps mmo, ala destiny or warframe… or just some kind of mount and blade type single player game, or even Conan Exiles.

The closest thing I can even think of is Raft - Stranded Deep.

… Its mad max… on the ocean, and is basically postapoc/dieselpunk.

Bang wow zoom, fairly novel game (by modern standards) for a AAA or even AA studio to try.