Well, I think a mod could make cities using the existing ksp space centers assets, combining the 3 tiers with the old KSC and the island airport, there is somewhat variety of buildings, repeating and combining them in some way, we should be able to recreate cities or other kinds of settlements, could even be procedullary generated by a seed, is not like the videogames aren't full of repeating buildings
I don't think I'm the first thinking this, but I don't find anything, and I don't have the skills nor the time for doing that, so I give the idea for whoever wants it.