Except this completely defeats the purpose. You no longer have a central DC supply, but instead have a wall-wart converter build into the wall instead of hanging off the plug.
This would actually be less efficient than the approach in the article, as you are increasing the number of idling DC supplies, not reducing them.
Ah. I was intending to comment more on the claim that electricans would install AC and DC runs (aside from most building codes and common sense requiring AC and low voltage unprotected DC to be run more or less physically separately) +5V switchers the size and shape of a light dimmer with a little USB port have been COTS for many years now, for dorms and hotels and stuff, so its more likely the electrician would run 120 AC to some convenient spot in the room where its converted to 12V at high(er) current rather than a parallel scheme where the electricians homerun both 120VAC and 12VDC to a combined circuit breaker panel or some such.
Or in short (oh bad pun), DC power supplies are COTS and electricians know exactly what to do with them.
It is inevitable if you had parallel wiring they'd mess it up. Wanna be home electricians are made fun of all the time for screwing up 3 simple obvious wires line neutral and ground, giving them +5 would just result in fireworks. Admittedly most of the electricians making fun of the home wiring guys are the same pros who blow up 3-phase machinery by swapping a phase on an occasional basis too...
Oh god. There's electricians out there that don't even know what 3-phase is. It's scary.
That and all the DIY guys building rotophases to power their cheap 3-phase equipment they got on auction, only to realize their 120/240 in their garage won't cut it.
This would actually be less efficient than the approach in the article, as you are increasing the number of idling DC supplies, not reducing them.