On a land tax, from the comments

A land tax in its purest form will never survive contact with political reality. To implement it you have to tell people that own their own homes that they are in fact renting them from the government, and at rates which depend on how much other people covet their land. This may be economically incorrect but it is how opposition will play out.

Furthermore, determining land values as distinct from property values in highly built-up areas with strong planning constraints (e.g. the UK) is an exercise in guesswork. You cannot realistically disentangle the value of the land from the actual and likely permissions on that land. The valuation process will be intensely political, prone to corruption, and any modelling easily manipulated by how exemplars are chosen. In the UK at least it would be a bloodbath.

That is from Sonofid.  And from dan1111:

So much hand wringing over NYC and San Francisco, and treating this as the standard “urban” case.

Meanwhile, 90% of US cities feature depressed urban cores with very cheap, under-used land. Maybe figuring out how to make more US cities desirable is the low hanging fruit? And there is plenty of comparative study that can be done, since some cities have been better at rebounding than others.