It needs to start somewhere though. Obviously you can't just drop a single building in the suburbs and call it a day, it should be many, with plans for public transport, axing the zoning code to allow for the ground floor of the building to be used for comercial purposes.
The problem is introducing the zero-setback designs organically - as the people there likely receive little to no benefit, and the people who do receive the benefit aren't there now.
E.g., a house could easily be fit between mine and the neighbors, but we wouldn't really benefit from the density improvements, and the family that would move into the "missing middle" doesn't currently exist here.
I'd love if our lot was zero setback, as I'd build an addition right up to the property line instead of having to try to find another lot/house in the area we want.