The massive living spaces we have now are not sustainable. By 2050 if we are to avoid 2 degrees of warming we need to be emitting 2 tons of carbon per year per person: http://insight.gbig.org/targeting-2-tons-closer-than-we-thin.... The average American today emits 11 tons, whereas 2 tons per person is closer to that of someone living in Brazil or Egypt.
In climates where you need to heat and cool a home, carbon taxes will make heating and cooling the living spaces we have now financially impossible. People will drive demand for these smaller living options out of necessity. Additionally, as we make consumption less and less economically attractive people will have fewer things to want to store anyway, and personal vehicles will likely no longer be something the average person will be able to afford or want so there will be less need for parking and garages.