This is an excellent point, but I don't think that zoning laws are a good fit for that. Zoning laws can be changed (and often are) by a town council or other go

This is an excellent point, but I don't think that zoning laws are a good fit for that. Zoning laws can be changed (and often are) by a town council or other governing body regardless of what the land owners want. A permanent easement that can be put on one's own property that restricts what one can do on it is much more effective, and is exactly what you're talking about (trading a development right). In my state we have many properties that are covered by conservation easements; these are permanent easements attached to the property that prevent most development and grant some state tax relief. It also obviously negatively impacts land value, but it's voluntary on the part of the land owner.