I was thinking about it too. We could easily use a light density map there, but one problem is how to make the transition to city lights map ... and then to individual lights.
... the texture overlay may be even used to reversely place the light-sources (not for a created location, but lets say as a possibility to displace urban areas by this "light distribution texture" at the further developed Urban area generator -- i just write this, cause there may be people, that would like to create worlds by its orbital night-light distribution, like recreating planets from StarWars, where cities are trough half of the planet, but little known on ground, witch could be taken by the procedural city-generation on the "light-distribution map" basis).
... also, i dont think, that if the map is generated at so 6-10 kilometers height, blending wouldnt be as bad, if the texture projection will be on the surface (that is, with all the terrain deformations).
Problem might be another - light-pollution as an effect of greater clusters of light hidden behind a mountain. This will be some interesting thing to include to OT. Specially when the light should affect clouds too !