I suggest Moons or satellites for planets as, many planets probably would have at least one moon (this excludes planets where their star would probably destroy the moon when it was on one part of its rotations). Think about it, in real life, we have a moon at all but two planets in our solar system, so it would make sense to have moons here. The main problem would probably be the lag from adding more things, so it could just be on a few planets which could have pulled asteroids from out of the system together to make a moon, then have been rounded over time, and is now round as it can be in Minecraft. Maybe these could be unclaimable, and have random assortments of resources such as chetherite, titanium, aluminum, and others. This could in theory solve the problem of all of Quod being claimed, as it would provide a few new places to mine for cheth. There could even be a moon that only people who started within the last month could use.
I am open to suggestions.