I envisage a quasi-ameboid faction where it's members actually form the buildings and improvements - and they would all count toward population.  The Molded would be the members of society that have taken on uses for the other members of society.  Sentient spaceships, living highrises, and other improvements are all voluntarily taken from the general population, called the Unmolded.  The faction has a strong social conscience, and social rank is determined by age and usefulness to society.

I'm intrigued, can you flesh this idea out a bit more? What is their faction affinity and traits? How do these encourage a diplomatic play style? See my submission and several others for a good way to lay it all out.