Believe me, I would like to convert the med-low poly stock ships from Bridge Commander and allow for everyone's computer to run it and in addition to that, massive large scale battles and missions. The problem is, I would be in danger of violating copyright legal stuffs if I use the models from a retail game. "Totally Games" would be on my ass for that one. And if such a total conversion were to get popular, I think they will notice it.
To play it safe, I mostly convert models made by other modders. The thing is, most of the modders made these ships high poly because Bridge Commander had polygon counts that maxed at around 2000 and had very low res textures.
I understand that ships must meet a certain level of playability for mission friendliness. At the same time, SCP is allowing for higher standards now since FS-Vanilla.