I don't get the obsession with size. I have a mid-tower PC in my living room behind the TV. If I had a Steam Machine, it would also go behind the TV. Why does it need to be a small cube? I get why you wouldn't want a giant full size tower, but there are plenty of small cases that can still fit a full size GPU.
Some have a nice living room with expensive furniture and a wife who doesn't want a metal box or that ugly PS5 in the living room. A small cube will maybe pass...