Yeah, thats something I've wanted for awhile...The developers said in one of the roadmaps (at least, I'm fairly sure they did) that they were going to work on the planet customization options and eventually add in the ability to import your own custom models and at that point I suspect they'll add the ability to use custom textures as it's logical to do so, but as for anything sooner than that, one of the devs would actually have to give an answer on that as I haven't seen anything yet.