Outside of an expansion or mod, I can't see anything really progressing here. There really just needs to be more advanced defences. Expensive so they couldn't be massed, but powerful enough to give even HCs a fight. Starbases and heavy defence platforms.

For what we actually have to work with, I would really just like to see defences scale better throughout the game. A turret works fine on a basic frigate, but once LRMS and carriers show up at tier 2/3 they're now useless forever unless you mass 20 of them. Weapon and armor upgrades should affect turrets more, maybe with a scaling cost to prevent extreme turtling. Like instead of a 5% damage bonus per research they get 10%. This would insure that you don't need 5 turrets just to have a chance to kill a lone HC.

I'd really like to see a flack turret, similar to the regular turret, but be very effective against fighters and bombers. It would make it more difficult for someone to crush the defenses with just a few carriers.