It would be great to have an image (or more) with the height of the cubemap in a black and white gradient, this could make the brush tool work only by painting in the image and that would mean that surfaces could be made in 3rd party software (like GIMP or Photoshop), giving us more posibilities without the need of complex ingame tools.
This way we could use real life data in order to make precise Solar System bodies.
possible data source
@NathanMikeska you can mark this one as solved