Land is fixed, but land-per-dwelling is not if you build more densely
if you do it over a whole city, i'm not sure it still holds. not as much, anyway, since the developers have more choices on where to build
NIMBYs did indeed get involved: you can build up to 4 units in basically any residential zone except for the "rich people" part of town
more cities seem to be doing this sort of thing. hopefully we'll have more/better papers on it in the near future. (and hopefully it works)
The most disastrous idea in urban planning is that prices can be kept low by limiting use, and trying to preserve "affordability" for a narrow slice of the middle class. It has failed entirely.