Yes, and they need to be flexible via public policy. If two generations from now some 10acre plot of land made into wildland is now surrounded by skyscrapers it probably makes a whole lot of sense for there to be a means for the local population to vote to remove that protection and turn it into affordable housing or whatnot.

It gets nuanced - but in general speaking terms this sort of thing should never be forever set in stone because someone alive 100 years ago decided as such via a private contract. Many other ways to go about setting aside areas for conservation.

Even conservation trusts make more sense to me. It’s still private, but they have an incentive to stay receptive to public comment and be a bit flexible. They might swap that 10 acres for another 100 acres somewhere else that creates a 1200 acre contiguous wilderness or what have you in order to stay relevant to contemporary needs while still staying true to the 250 year old mission.

I simply do not think you should be able to dictate (via private means) what happens to a property after you sell it. That’s for the next person who owns it to decide - in accordance with current local zoning and land use guidelines.