Start.
Ships are great, I suggest like, specific roles or different models of one class
Instead of Tek, do Steam Tek. Like with modules that let you live undrwater by sucking out water n making O2 (and it needs fuel so its not op)
Divers with underwater mines n such raiding a highly valuable underwater player base sounds bad ass as all f get out.
(will update as more ideas come)
Feel free to add up mates