being able to actually build the majority of a base underwater like TA.
Imagine Setons with a base tucked away in the corner
IE- power gen , mass/e storages, proper underwater torp defenses, anti sonar tech (ala stealth field gen), floating cloaked limpet mines, being able to seed low cost sonar perimeter lines trigger when crossed (single use), underwater walls that can't reclaim/destroy barring a nuke (no rust in this universe)
Hydro plants upgradable to T3 with a small shield
Limited amount of mass/e storage (10?) to build underground but costs 3x current storage
T2 torp boats are trash, make them subs
I like arma's suggestion, engis on patrol can reclaim to inflict damage