Also I just thought of something. Even if you could make a Sith Alchemized ship, it would be totally imbalanced. Never wears, can't be cut by a lightsaber wielding boarding party, absorbs energy like sith lightning (sometimes for later usage) and it reflects/absorbs all blaster bolts. The only thing left vulnerable on the ship would be its engines, which I guess balance wise would be okay since it's main mode of attack relies entirely on the engines, but it would be min-maxed to the extreme.
That's not even taking into account of structural damage upon battering another ship, or the colossal weight the ship would have. You might be able to find some tech reason why it could handle the impact, and you could say that all the occupants are droids, but how in the world are you going to find engines big enough, and reactors large enough (or numerous enough) to even keep this thing in simple orbit? It would have to be permanently a deep space vessel, lest it get too close to a gravitational body and crash.
Of course, that's only IF you were capable of getting enough alchemist masters to devote their time to this singular project for IC years, as Val said. The dev thread(s) would be stupidly massive. Like, probably bigger than what is currently required for Flagships.