in particular, there's no trace of civilization
This, especially on the night side! City glowmaps - especially if they could be linked to population size (and maybe tech level too, depending on whether you imagine TL1 to be stone age, or current Earth technology, or somewhere in between: personally I favour the stone age end of things, as I think it makes for a more interesting imaginary universe).
Now this is an interesting idea... However some things need to be taken into account: planet size, landmass locations, tech level, and population numbers. For example one of the higher TL planets can have a number population centres (cities), determined by a random number generator. But since that would be a high TL number, the number of cities shouldn't be below, let's say, 20, and not higher than 40. Through the rendering mechanism for planets, I assume one can figure out where the landmasses are. Then, generate a glowmap or transparent texture of some kind which places the cities at certain spots. The trick now is to keep the cities at the same spot for each planet.
An alternative is to have transparent PNG's with pseudo-shining spots pre-rendered once, and "overlay" those on the existing planets. Since there are "only" 2048 planets in the core game, this number of mostly transparent PNG's wouldn't use up too much space.
This is coming from someone who does know a little bit of programming, and these would be the two approaches that come to my mind.
I suggested the night lights thing before. Apparently it needs (one more) shader. That would be a major advertising feature for 1.86 imho, that and the improved atmosphere shader.
Before we think about the size and the places of the city, we gotta find an efficient way to add them in the planetary texturing stuff, which actually already generates two 2048x2048 textures (land and clouds). But I think that in order to get a satisfying result, one would have to switch to 4096x4096 - four times more pixels. Except if one also switches to 2:1 aspect ratio that reduces that to two times more pixels. I'm running this config on an Intel i3 and while one experiences a slight "hiccup" at launch or at witchspace exit, it's definitely worth it. The textures look better near the station.
For cities I believe one has to generate yet another texture to be overlaid on the terrain texture. In my attempts to use the land texture generator, simple methods make cities "hug" the coastlines or the centre of continents. Not very satisfying. And one cannot perform complex computations when it's per-pixel. Certainly more satisfying results could be achieved by overlaying a "cities" texture on top of the land texture. I think that even "tiling" nebula textures or stars textures could work, as oceans and clouds should be enough to "hide the trick" - actually I believe that it could look better that POV textures, which don't benefit from shader magic.
Gotta dive deeper in the OOlite engine and figure out how to do that.