I tend to divide recreational pilots into two types: rag and tube pilots who tend to have day jobs in the airline world, and mini-airliner pilots whose day jobs are in IT. A simplification, but there's some truth in it.
Whatever their numbers, when fully automated mini-airliners do become available, only rag and tube pilots will remain. And only then to the extent that airspace permits.
I think a big reduction is inevitable as we draw away from the era of heroic aviation. Also, demographics dictates that people of my age and younger have far less disposable income, and I gather other hobbies such as sailing and golf are in similar decline.