> one thing I've always wondered about Georgism and Land Value Tax is whether land supply is actually inelastic

It isn't actually perfectly inelastic, but looking at land reclamation (and erosion!) relative to the ease with which places to live can be added to a locale, the supply of land is relatively inelastic. Even then, that kind of misses the core of George's argument about land value.

George himself distinguished land from labor and capital by looking at it through the lens of whether the economic value of a piece of land needed to be attributable entirely to improvements undertaken on that land. This is his "all natural opportunities or forces," and those are where the constraint lies.

For land reclamation in particular, there are two things to look at: (1) the value attributable to the land reclamation effort; and (2) the residual site value. (2) is land rent, and the Georgist model really is predicated on the relationship the surrounding community has with a piece of land. As it goes, if the community's feelings toward, say, a reclaimed waterfront are tepid, that reclaimed land won't have much value (even if the land reclamation were undertaken at great expense!), and won't command high land rents.