I agree that gathering people into larger population centers is way more efficient for us and the planet, but I don't think anyone's arguing for us all to spread out on 10 acre farmsteads.
The middle ground is just to build more decently-sized cities in all of the vast available land. Why fight for overpriced artificially scarce land in San Francisco when there are 20 other SF-equivalent cities a state or two away (existing ones, or ones that could be hypothetically built). "Location, location, location" has got to stop being the reason people choose a city.
As a side bonus: by moving a bunch of coastal persons back into the flyover country, you're re-exporting newer cultural norms into those backwaters, perhaps enough to cause meaningful cultural and political reform in places that sorely need it!
Why? I want to live where I get to do the things I enjoy. I would say most people I know prefer temperate, low humidity weather, access to fresh fruits and vegetables, beaches, mountains, lakes, good water quality and security, etc. The places that have these features will cost the most, since more people will be bidding up the price.
I think you massively overestimate the rural "subsidies". Make it easy to move rural and "go green" with minimal regulations, and you may find the problems nearly solve themselves.
Western Washington state subsidizes Eastern Washington state greatly, and that isn’t even as sparse as South Dakota (or as I like to call it, Tropical Dakota).
World arable land is ~26.2 million square miles, or about 2.2 acres per person. At 11 billion people (projection world population peak by ~2100, you get about 1.5 acres of arable land per person. There is literally, physically not enough space on Earth to put your plane into action.
I like nature, but I think you underestimate the subsidies given for rural development and infrastructure and just how unsustainable our development style in the US is.
There will soon be 11 billion people in the world.
This is a pipe dream, but if it came to fruition it would wreck the planet very quickly.
Running water? Gotta run the pipes further. Road access? Gotta pave (and maintain) more road Power? Same thing
Plus having decent response times for emergency services, quick commute to things like groceries as you mentioned.
Not to mention having critical mass for a commercial district with any sort of variety within reasonable distances of each other to compete and cross-pollinate.
People don’t expect just electricity and plumbing, they also expect modern construction techniques, roads, police, fire suppression, emergency response, schools, full-service hospitals, telecommunications, airports, parcel delivery, ....
A big reason that rural / exurban living is cheap in the USA is that we massively subsidize services for people living very spread out.