Now I've got a mental image of some poor bastard actually attempting to construct a base out of lithium ... underwater. It is, if nothing else, funny in a Looney Toons sort of way.
Something that would be cool to see eventually would be the removal of health regen as something you start with in place of a med-bay where you can heal yourself up and use local resources to create a med-kit of sorts to use on adventures. Anything …
A moon pool for the seamoth and mech suits should definitely be a thing but for larger vehicles a jetway/docking collar set up where you park outside would be more appropriate I think.