the incremental cost would be good to ditch..
This is interesting, but id never use it myself. I do like the concept of having a different twist on hull upgrades if the hull is going to get this high in number however heals with a mine layer would begin to take a long time.
Maybe an upgrade featuring reinforced hull, to give more hull health and a damage resist with the same mechanic as hardened shielding. % reduced damage and maybe a cosmetic change to the armor of the ship along with it. this upgrade would be a good counter to a team focusing kinetic use or destroyers with the hull damage research as it would % decrease the amount of damage taken to the hull, but i dont see a reason to make the ship grow or to decrease its speeds.
Personally though id like to see boarding happen before any of this

these awesome ideas will only hinder the speed at which boarding is released which will complete the map and open a new avenue of offense and strategy.