Sure there's loads of terrible land in West Texas, which could possibly provide for a lifestyle of subsistence farming, but the US standard of living is such that it would be wiser to live on welfare in a city.
But in theory, if someone could covertly farm some crops on one of the numerous vacant sites in Manhattan, and not have to pay any rent, then that same amount of subsistence labor could provide for a potentially decent lifestyle.
Same amount of effort would bring in a much greater return, just through the better location.
My point about farming was to ask why we can't all share in the fruits of rising productivity. Why can't we just keep doing what we had been doing, and still take advantage of fancy new gizmos? And the answer is that progress causes land values to rise, but the valuable land is generally owned by a subset of the populace who demand a greater and greater rent just because they can.
So really the question is: how can we all share the value of land, without it just funneling back to higher rents? My suggestion is to look at land value taxation.
Rentiers are just the current solution that forces farmers to work til Friday. The problem is that trickle down doesn't work.
Land value tax just makes everybody rentiers and racks off the farmers because they get nothing of exchange value in return for their week of labour.
As for everyone being rentiers, I'm not sure I see the problem. Everyone being rentiers ensures a minimum standard of living, allowing us all to share in the progress of civilization. But really, land value taxation itself raises the "margin of production" even without any kind of redistribution.
The mention of trickle-down seems like a non sequitur.
It's also pretty clear that some sort of resource footprint is more interesting than apparent living density. Just food requires more than a few hundred square feet per person and we consume a lot more than food.
You'll have to qualify that statement a little. Here is 5 acres of land in Texas for $1500 [1], found it in about 60 seconds.
[1] https://www.zillow.com/homes/for_sale/TX/land_type/209109538...
If you want to do brass tacks or whatever, buy it and scrape out a living to prove that cheap scrub desert makes a point about land being available.
Obviously water and other resources are going to be an issue, but as a labour multiplier, AI and robotics have huge potential.
Then that land (if not already privately owned and actually available for homesteading) will be homesteaded, privatized, enter the land market, and not be rent-free land that is available. Just like the land that was attractive for homesteading in the past has been. Sure, its a one-time land-rush just like the initial homestead act, but after that the same forces of centralization of property that always work in a capitalist economy will work on it.