I'm not saying I agree with this forecast, but what may be zero in decades to come will be public tolerance for general aviation. It may not be a prohibition, but that a lack of public tolerance, and facilities, will make GA very expensive. I know that the vast majority of residents in the Toronto area are not the least concerned about the loss of three local GA airports I have flown out of in past decades, with two more in real jeopardy. And that's only for the land value, nothing to do with pollution from airplanes. GA will be around for a time to come, due to the efforts of dedicated owners, but it won't be as common as I recall in my youth. It'll be a lot more effort and expense to fly in the decades to come, and some pilots won't continue to make the effort against public shaming. Once the drivers of huge car and non essential trucks, recreational boaters and other non essential petroleum users, begin to be restricted by environmental concerns, they won't step up to ease a path for continued GA operations, while their own toys are grounded...