They are basically recreating the size of a metro area efficiency apartment. Nothing that radical. Not denigrating them in any way, just saying they are not on the cutting edge of anything. The "green" appeal is what makes the story.

The only thing that can be prohibitive is what the building codes say for size. Where I live about the smallest you can go for a stand-alone structure to live in (plumbing/electric) is 180 sq ft. We had a guy here build a 15x15 house in town. It is pretty slick.

Anyway you look at it it is still a cool idea.