[Game Idea] An Underwater Region

The title basically sums up my idea. Imagine an entire region that takes place underwater! I imagine everything would be concealed, much like Bioshock, except you can explore outside and into the water to get your water types, maybe with the HM Dive.

I only have a few ideas for something like it, namely that it might be called Pokémon Atlantis, and that the evil organization would be called Team Trident. I also like the idea of this team specializing in Ice types.

I'm not planning on making a game like this any time soon, what with Pokémon Nebula's current development, but I would love to hear some of other people's ideas for the game. Thoughts? ^^

HMs are old news but I actually do like the idea. It'd be neat to explore the lore of the region- like why it's underwater in the first place. Maybe it was built to be a Libertarian paradise like in Bioshock, or maybe by some ancient civilization?

I like the idea, you could name the region Atlan. And than implement some Atlan Pokémon forms similar to Alola.

very cool idea. I feel like if the entire game was under water it would be boring. But if say 60% was under water but you still could go on to land its a cool idea.

I think it's possible if you do a similar concept with underwater caves. This allows you to split them into dark caves for (bug, grass, dark, fairy, stone, ground, fighting), volcanic caves (fire, steel, ground, rock, psychic) & domes for flying, normal, electric, etc... You don't really need land if you work like this. You can even do an ice caves add the other side of the region.

If someone goes with this idea, I would much rather see a continuation of R/S/Es story. Team Aqua has successfully awakened Kyogre and expanded the worlds water. There could be a ton of great ways to tell a great story. Perhaps Archie has become a tyrant of sorts with the power of Kyogre, and taken control of the gyms and E4. Maybe you end up working with Maxie to try and put a stop to it. Maybe seeing the damage caused by Archie, Maxie has come to realize that balance is necessary. Or maybe he seizes his opportunity with Groudon (probably needed to stop Archie's Kyogre) and expands the land, throwing the region into a complete drought. Suddenly you either have the grounds (no pun intended) for a sequel of sorts or just leave it as a fun twist that goes unanswered.
A new underwater region with a new team would be cool too, though. If done well, of course.