To me, this feels like a solution that's looking for a problem. Being able to get a faction's ships by attacking them & salvaging them isn't even a bad thing to begin with, and even if it was a problem, tying it to blueprints causes so many new problems. Now your ability to get ships post-combat is so heavily tied to RNG from getting the blueprints in the first place that it's functionally impossible; a method of getting ships that works best in the early- to mid-game is now exclusively available to the ultra late-game, at which point you should be able to just build whatever ships you want anyway since you already have the blueprints for the ships you want. You could always try raiding for blueprints, but doing so is inordinately expensive and tends to just get you complete junk. Who doesn't want to spend 2000 marines raiding big military worlds to get a Kite (S) blueprint and nothing else?