I don't know how the game itself will turn out but I think a have an
idea so far. You will get to pilot a hi tech submarine in an alien
ocean world and finish missions given to you such as exploring
underwater caves to collect rare materials, assisting the construction
of underwater bases (so that you my buy better equipment,) fighting
off attacks from the local ecosystem and other alien encounters, or
all three.
In game it will just be a square map with a system were every "tile"
is a set of tiles layered over each other in a way that could be
compared to RLE compression and that should give a sense of depth to a
large game world without using tons of memory. It would also allow
things like underwater caverns.