Even if you had no zoning or "organized" NIMBY restrictions, it would be extremely slow to build denser in the most popular "full" residential places: any new construction there requires someone else to sell and leave for that construction to take place. You aren't going to be able to build a hundred-unit tower like you could if the land was empty or was just a vacant old structure.
Targeting stuff that isn't currently residential would be a much easier starting point.
IMO, but more controversially, it goes even further: in the long run, especially with fast transportation and digital communications, it's hard to see certain places ever getting "affordable" given today's wealth distributions. Some locations are going to be in higher demand due to non-human-development related factors (weather, scenery, etc). Others due more to development factors: NYC is more in-demand than if it was an empty bunch of land because we've already done a bunch of development there. (That latter case is especially interesting because it shows how development can both increase supply AND demand, it's not solely something that affects supply.) So if some places are inherently going to be more in-demand than others, and you build more when the market price is currently $X, prices won't fall very quickly at all as you get the people who otherwise want to live there, but couldn't do $X but would do it for $X-1, $X-2, etc, now re-interested in the area!
> Others due more to development factors: NYC is more in-demand than if it was an empty bunch of land because we've already done a bunch of development there.
Agreed, and human development is a major part of that. NYC is a cultural center of the world, which is a result of its human development, and that has a tremendous currency and gravity over and above Manhattan's physical grid.
Targeting stuff that isn't currently residential would be a much easier starting point.
IMO, but more controversially, it goes even further: in the long run, especially with fast transportation and digital communications, it's hard to see certain places ever getting "affordable" given today's wealth distributions. Some locations are going to be in higher demand due to non-human-development related factors (weather, scenery, etc). Others due more to development factors: NYC is more in-demand than if it was an empty bunch of land because we've already done a bunch of development there. (That latter case is especially interesting because it shows how development can both increase supply AND demand, it's not solely something that affects supply.) So if some places are inherently going to be more in-demand than others, and you build more when the market price is currently $X, prices won't fall very quickly at all as you get the people who otherwise want to live there, but couldn't do $X but would do it for $X-1, $X-2, etc, now re-interested in the area!