They're planning on doing more with the ocean, yeah. They also did just add fish.
A secret ocean boss would be really cool, but how the fight would actually go, I have no idea. If its threatening to players, it would likely blow your ship up which would be the end of the fight, and its not like you can repair it or anything way out in the ocean.

Maybe you kill the boss over the course of the entire game, it just appears randomly in the ocean and you chip away at it before escaping. The boss never healing up.