hmm.. I'm not sure much of the HN crowd cares to run Win8 on any sized PC, interesting nonetheless.
You can really run any OS you want
I really don't ever want to buy a trash can size PC again. Is there some reason that we can't make most PC's the size of the Mac Mini? Just throw out as much legacy as possible and make a new sweet standard. A new video card standard is probably the hardest thing.