Still pretty cool though.

Never underestimate the ability of a home tinkerer with too many tools and not enough common sense (or electrical education) to do things you previously thought impossible. And.... like I said, amateur electricians plus DC in the walls = entertaining reading!

Modern switched power supplies aren't bad. The only problem is that there's no standardised connections. (Or rather that there are too many standards...) Surprisingly USB is starting to become a standard for 5V up to 1.5A.
All we need now is a similar standard for 12V (preferably up to, say, 5A). I'd propose the Molex floppy connector, but it's probably too expensive. The sata power connector is probably cheaper to make as it's just an edge connector.

Plugpack circuitry integrated into every power point? One big switchmode DC supply in the basement and chunky wires to every outlet? Separate solar-powered grid-independent circuits? I don't think there's any really elegant way to do it.

At least with AC it makes you let go when you get zapped. Or so I've heard... I mean not that I have any personal experience here.... no, we will not discuss the tweezer incident when I was 8. Besides, it wasn't that big a fire and we needed a new TV in any case.

There's no real problem with making a computer in a cardboard box or with all of the bits hung on the wall or whatever - it'll interfere a bit with nearby radios and TVs, but won't be a serious interference source like, for instance, an old-fashioned spark-gap radio transmitter.

But it's still, usually, very much illegal to actually sell such computers. Cases with windows in the side may be technically illegal, too.

(I've mentioned this occasionally in reviews, like this old one.)

The solution to the problem of conservation of angular momentum is to use counter-rotating blades. Of course, that would only add to the mass/complexity and increase the fixture support problem, but that could be solved by the rotors constantly spinning to generate lift for itself...