So, this is what happens when i combined two of my favorite games together.
Both games are running at the same time on my PC
Space Engineers handles the planet, the grids, the physics, and your character and it stays fully playable, everything you can do in SE, you can still do it here mods included
Subnautica handles the ocean, the graphics, the creatures, all of it
When you fly down to some point (1000 meters) to the water, the view switches over to Subnautica and everything you built — your ship, your suit, whatever else — gets mirrored into it. Underwater, it's Subnautica's world, that you can build on and many more soon.
This is raw gameplay, about 14 minutes, no editing
It's still a work in progress and not out yet, most of the things you see will probably change.
I've got few more things to polish and to test before releasing it