Yes, I've seen this sort of thing (cut of any future price rises due to housing development) several times in UK agricultural land sales. If I'm looking at buying land from someone with this idea I try and explain that in any commodity business if someone wants to buy a call option it has a premium; which in practical terms comes as a reduced price for the land. 9 out of 10 would-be sellers don't get this (and presumably have many people backing out of the deal as a consequence).

However two parties can agree to do any (legal) thing in a contract, and if one party fails they can be sued for damages. We can agree to give you a cut of future sales, or not charge a rent below X, or paint all the grass blue. Always read the small print...

Regards

Mark