I've actually never heard of it as a commercial industry before; not at least beyond immediate community stuff. I've always encountered it in places that talk about homesteading and maximizing space utility (especially for urban places, but even out in the wilderness people use it to recycle as much as physically possible). Has anyone tried/do they do it on a commercial scale, or is that just conjecture, or stuff people talking shop go on about with awe, longing for the day it becomes feasible?