If they could gather enough capital to buy enough land and build enough in a neighborhood to allow this, they get part way there. Commercial buildings, such as small corner stores, daycare, etc. would still be banned in purely residential neighborhoods.

US planning is really abysmal and detrimental to quality of life, and it's nearly impossible to get people to even realize it because of car brain.

I'm hopeful that we can adopt eco-districts in some area and start to turn this around, but it will be a 50-100 year project to correct US planning.