Intrinsic Celestia DSC spheres for showing a "backdrop" would be very useful. They could be used for showing high-resolution textures of things like the CMB or galactic panoramas. I'm assuming they would support arbitrarily large surface texture images and VTs like the current SSC and STC spheres do, but would have inward pointing surface normals so their textures are only visible from the inside. The use of a Mesh with backdrop images forces them to be scaled down to 1K for hardware compatibility, producing very poor results.
As an alternative, support for true backdrop images (always behind everything) might be reasonable. Presumably they'd have to have the same orientation functions as DSC objects do, since appropriate all-sky images often have strange orientations.