[brudgers]

" This could theoretically fit 1/6 more people into the same amount of "square land" without any drawbacks other than cosmetics."

In the US, the primary constraints on density tend to derive from land development regulations - particularly those relating to parking (non-surface parking is expensive), direct limitations on density (dwelling units per acre) and limitations on overall floor plate area (floor area ratio).

Overall building height is somewhat uncommon as a constraint on density and tends to play less of a role than floor-area-ration in determining how much space can be built.