In all our long investigation we have been advancing to this simple truth: That as land is necessary to the exertion of labor in the production of wealth, to command the land which is necessary to labor, is to command all the fruits of labor save enough to enable labor to exist.
Emphasis mine. The capitalists want it all, even the little that has been reserved for the reproduction of the worker. George goes on to finger finance capital as well:
We have been advancing as through an enemy’s country, in which every step must be secured, every position fortified, and every by-path explored; for this simple truth, in its application to social and political problems, is hid from the great masses of men partly by its very simplicity, and in greater part by widespread fallacies and erroneous habits of thought which lead them to look in every direction but the right one for an explanation of the evils which oppress and threaten the civilized world. And back of these elaborate fallacies and misleading theories is an active, energetic power, a power that in every country, be its political forms what they may, writes laws and molds thought—the power of a vast and dominant pecuniary interest.


The value is defined the same way we currently do it for property taxes, there’s no real change needed there.
There is already an option to give up land, and yes that should continue. The government can just take it back and sell it to someone who wants it.
Yes, it would discourage the use of land for unproductive purposes. For business purposes (which I assume is what you’re talking about) businesses that need large amounts of land would likely just be further out from the most desirable land locations. In desirable areas, multi-story offices, malls, etc. would be the norm to handle commercial uses. Strip malls and massive parking lots can die a horrible death and I would be pleased as a peach.
As for the income tax thing, that really depends on your jurisdiction. The amount for the UBI would directly be set based on the amount of the tax to offset a “normal” usage of property, a family of 4 in a 3-4 room townhouse in a city shouldn’t pay any more under the new system. A family of 3 in a condo would probably end up with more money, and a retired couple in a detached house near downtown would pay significantly more (or likely sell and move). Some ultra-rich jackass in a mansion 20 minutes from the core would just have to pay to keep the privledge of doing that.
This system doesn’t remove the ownership aspects that come with private property, which means it provides people with choice and control that would be lost with a socialized/government run housing system.
At the end of the day though it encourages more efficient use of land, removes investment in land for speculative purposes, and by both reducing prices and removing income taxes and/or UBI benefits working people over investment/capital.
Overall I think I get your point, but how would a socialized housing system remove choice?