With 29$ for what used to be called a "family pack" and a permissive license regarding virtualisation, it almost seems like Apple is taking a very different position regarding the Mac OS. That it's a way to sell Macs, not to make more money.
This would be useful, but even on my hdd I haven't the room. Features like this are why we need ssd+hdd (unless they expect it for 500gb ssd macbook pro and mac pros only).