I added a feature to the engine: if real (catalog) planet has only height map defined (like Venus and Titan), then the color map is being procedurally generated from it. I need a reverse feature also - if there is only a color map defined (satellites of gas giants), then the height map is somehow generated from it. The easiest way is to convert the color to black and white and take that as a height. With the help of such a cheat, I can reduce the size of SE distribution by 50 MB. Anyway height maps for Io, Europe and other moons are artificial.
The logical continuation of this idea is procedural improvement of level of detail on real planets. I.e. generation of finer lods that do not exist as textures on the disk using existing upper-level textures as first octaves for noises.