1) I think pseudo real-time cloud cover information on the earth would be insane. (and useful!)
2) Is it possible that as you approach the earth (or other planets), the standard planet texture could morph into a more detailed one? IE.. As you get close enough to earth, standard textures could morph into a image that comes from terreserver or something that shows hi-res images of terrain. Obviously, the user would have to select only certain regions for which the data is available for memory or storage considerations.
3) What about the ability to 'land' on a planet? The eclipses might be cool to watch if one were standing on a surface at some given point. Even cooler (along the lines of #2) would be to use some generic surface textures (earth or mars only I suppose) so when I'm standing on the surface, I can actually look around and see what I might see if I were there. Watching an eclipse from the surface of mars (are those moons big enough to eclipse the sun? I dunno) could be cool.
