Have you thought about adding a way to expand or explore the sea. There could oil in the water which you could pump and make oilrigs and build into sea.
To make it more balanced there could be aliens that live on water to bully the player and harass. Boats or/bridges could be a nice addon too for ...

Hello!
Me and my friend tried to connect to eachothers game but we coudnt connect. it read that but it failed after a while. if someone could help me or link something that could help.
Thanks in advance !
-Jazka