Well, that requires (to some degree) majority support for the subsidy and thus the thing. If a minority (or even just 1 person) has a patch of land, and is perfectly sincere about want it to be less-than-maximally (financially) productive, they will have to pay the full price.
It's true that this problem doesn't arise under Georgist tax policies (AFAIU) for public land, so there's that. But I still feel a little uneasy about making land preservation by individuals prohibitively expensive.
> land preservation by individuals prohibitively expensive.
Only if that land preservation is in the middle of the city ("land preservation" that typically looks like gated-in parking lots). Nature access can and is subsidized in the city.
It's true that this problem doesn't arise under Georgist tax policies (AFAIU) for public land, so there's that. But I still feel a little uneasy about making land preservation by individuals prohibitively expensive.