At the rate things are going it would take decades to get everyone exposed, but much less time than that to lose natural immunity.
The only Americans who might be vaccinated in the future but aren’t vaccinated today are children under 12. The FDA is in no hurry on this because it doesn’t make much difference anyway (minimal vaccine risks loom larger next to minimal COVID risk).
I think this is a slightly-too-bleak-for-the-evidence take, because it's not clear how long immune defense persists. COVID antibodies tend to go away kind of quickly, but there are (so I hear) other mechanisms of defense which may persist longer.
Things could of course be much worse - it's possible that the COVID molecule is somehow unusually well situated for immune escape and length of immunity won't matter that much; those of us in countries that can afford it will get our semi-annual microchip infusion with the latest flavors.
The only Americans who might be vaccinated in the future but aren’t vaccinated today are children under 12. The FDA is in no hurry on this because it doesn’t make much difference anyway (minimal vaccine risks loom larger next to minimal COVID risk).