This law actually exists in Oregon and parts of Minneapolis. ADU laws were only in Oregon and Washington until recently, California's State-wide ADU push was part of a nationwide reform towards ADUs. The same is happening for SFRs.

Our federal governance structure doesn't provide enough $$$ for housing that isn't single family homes—until we change that, infill single family development is inherently subsidized by fannie and freddie -> I anticipate that other desirable areas will have to do this to stop out-migration and stay affordable.