I bet it has been suggested, but I was unable to find any information on it via my search.
I love the idea of a planet/comet coming into range of the ring planets and being available for a short time. These planets would have different colored dirt/leaves and would be a chance to explore/gather that resource.
It would be a fun chance to get excited about exploring and gathering new resources and having the planet ores/gems be a mystery! Maybe even mysterious gleam!
After the time, it would be out of range and all beacons/portals would stop functioning and it would no longer be available.
I know this would probably fit better after 1.0, but I think it would be super cool!