It'll never happen. If we're really that worried that humans won't have places to live, we'll build on green belts. It's that simple.
Edit: forgot to say that I am equally horrified. I would hate to live in that tiny space, and your toilet next to your kitchen...doesn't bear thinking about.
"Never"? Green belts are not infinite. There will eventually be a time when we run out of space, the population is increasing. Probably not our lifetimes but to say it'll never happen is foolish.