I found this very interesting. My parents haven't had a couch since their last one (ancient garage sale piece) fell apart when I was 10ish. My mom did make some awesome cushions out of an old foam mattress, though, about 2.5ft x 4ft x 3 in maybe? We'd lounge on those while watching movies. Or build forts. Our LR was generally pretty empty so there was lots of space for dancing, wrestling, somersaults, etc. Good times. :) I'm perfectly comfortable sitting on the ground, not sure if it's from our living room or numerous camping trips and general un-fussiness. I do actually strongly prefer to have my knees above my hips...and as a short person, that doesn't happen for me in most chairs! I also loved that one family's jungle gym in their living room, that was awesome.
Nonetheless, I do think it's a responsibility of parents to teach their kids mainstream table manners, which would be hard without a table. I also wonder about the biomechanics of activities like eating off a ground-level plate (particularly non-finger foods, like soup), or of doing artwork, writing, reading etc. (since you have to hunch over or arch your back up significantly to accomplish this...I was always discouraged from doing it for that reason, which worked for everything except reading). Sounds like the Bowmans' kids are too young for this to be a real issue yet, but I am curious what the plan is.
Going back to "tribal" forms of movement would probably be good for our bodies, but can only be accomplished to a limited extent in today's society, I think, in terms of our need to learn and do certain tasks like reading, writing, computering, etc. Which is by no means to say we shouldn't try.