Hello!
First off I want to make this clear: I am not a modder, and I have no experience with coding or any meaningful knowledge on how the SupCom engine works.
Now. I have ever since I began playing FAF been thinking that one thing that could be really cool is to make the water/oceans a lot more interesting. We all know how it works now, the water is a sort of compliment to the main theatre of war; land. Even on maps like Roanoke or Seraphim Glaciers you go across the water to kill your enemy's base which is on the land.
What if we did what they did in C&C Red Alert 3 and allow a bunch of different structures to be built on or under the water. Mass extractors, power generators, mass/power storage, air factories (And land, for floaty units?), TML, SML, SMD and so on. I am sure in the current balance, this could cause a lot of problems, but I certainly would love to see this tried as a mod.
(Slightly related question: If we have amphibious TMD like we do now, why is there no amphibious SMD? TMD stops both cruise and tactical missiles, both which can be fired from naval units (cruisers/Tempest and nuclear submarines) SML's are fired from nuclear submarines and Seraphim battleships...)