I wonder if prescriptive easement applies to the land owners that you talk about as climbers have been using the land openly for years and no I'm not talking about the Mohonk Preserve but the climbers themselves??????
This idea floats around every once in a while. In my view, nothing could be more foolish. The left half of Millbrook is on private land, as are all of the Bayards, the middle of the Nears, and all of Skytop, and many other less prominent crags throughout the region.
What do you think the impact of a climber's prescriptive easement claim anywhere nearby will have on access to private land?
Private landowners that do allow climbing on their land do so as a neighborly accommodation. They are being gracious in allowing you to use their land. Any climber claiming a right to climb on private land because they have been graciously allowed to climb their before would be a poster child for the selfish, ungrateful, entitled, and woefully disrespectful climbers out there.
Nothing would have a more deleterious effect on climbing access in the Gunks, and perhaps well beyond the Gunks too.
Brilliant idea. (Heavy sarcasm intended.)