I think we should have a phase where maybe the cycle is quicker to help you test out some things and get data. Then that cycle would normalize to a bit slower. I also think there needs to be breaks. Having worlds constantly come and go might be too much and then it would become just an average feature. Having some type of break or even a week go by without worlds keeps it random and feeling more special.
I lean toward worlds that go away fast and worlds that stay much longer… I’d love to see how planets change as they get mined with no ability to regen. I would link it to resource percentage left on deciding when the world goes away… maybe for the rarest items the world would stay until all of them are gone.
Lastly, this will be very controversial but I think you need to watch metrics on who is playing on these worlds and what is being mined and taken. This gives a sense of the distribution of these special resources to the WHOLE player base. We already have huge issues with scenarios where people are locking down resources so they can corner the market and ruin the game for many players. I think with these super rare resources they will be all mined up by these people and no one would get them unless they pay a lot of money. We need to balance that aspect of the game more.
Maybe a character is only allowed to stay on these Exo planets for a set amount of time per week or month. If they visit it too much they can’t stay there any longer and need to give their character time to heal or whatever. So when new worlds spawn they won’t be able to get on them because they spent too long on the other ones. This would then allow other players that maybe aren’t as high a level, don’t play 24/7, etc the ability to get these resources that would otherwise be taken.
If you don’t find some way to balance people getting the stuff that aren’t in game, you will just have another game feature that people won’t use much and more bad reviews about core players getting all the things.