Is there something similar to this ship allocation that needs to be done with planets to address planet buyouts?

Yeh. If you want to up the planet limit to 30k and
apply the same concept, it would probably work.
Might need more than 50 planets per corp tho.

Ok, so there's already a much higher expected number of planets in a game. 40% of a 30K universe is 12K planets. So that only leaves 18K planets for a reserved pool, assuming the 12K planets is a shared pool. With 2 planets per player for personal, that leaves only 34 planets per Corp in the maximum case of 500 players/Corps. So initially, that's going in the wrong direction. To guarantee 100 planets per Corp and 2 per personal, that would require a reserved pool of 51K planets. Not reasonable.

Of course, this is based on a 500 player theoretical maximum. So maybe it won't be ideal for a game that's set up to support 500 players. But why would you do that? Set it up to support 100 players and these numbers change to 12K plus 200+10000 for a total of 22200 planets, well within limits. So I think it would be practical to support something like 2 personal plus 100 corp reserved planets. Would that be enough?

Basically, the reserved planet pool would need to be dynamic based on the player count in order to avoid overrunning the 30K hard maximum. It could be 100 (or whatever is best) unless it needs to shrink based on player count. So worst case is it would be 34 planets per corp, but typically it would be the intended number of 100 or whatever.

Rather than basing it on the max corps, can you base
it on the corps currently in the game? Since most games
have a player expiration date, people that haven't been
in the game for months would naturally time off and their
slots would be open to the bigger corps.

In practice, we won't have 500 corps in a game. I've
never seen that many.

Oh, I agree that 500 is a pretty silly maximum, for players, much less Corps. Never gonna happen. I think the reality is, we have plenty of records to allow plenty of reserved records. I'll work out the details.