I think they really need to come up with a DC standard for home electrical, in addition to the existing 120/240vac standard. LED bulbs have step down converters as well as rectifiers (the good ones anyway). If there was a standard for DC light sockets you would only have a single converter with it's own breaker box and it would drive all the DC stuff. LED bulbs would pretty much be just an array of LEDs with zero electronics. Perhaps some could have some electronics like temp sensors but you could pretty much have just a bunch of LEDs. In fact this DC standard could extend to things like computers. So many things today use AC to DC adapters, so why not have a DC standard in the home. Basically it would just be a new light socket type and wall socket type.
At first you'd end up having to use retrofit adapters but as you rewire stuff you could add the DC outlets/sockets. 48v would probably be a decent voltage as it would not require too big of cables.
While I see what you are getting at in that it would be more efficient to have one place where rectifying and transforming is occurring, it will still be wasting power at the conversion site. Coupled with running extra dedicated wires, and you are not really saving much. This effect is compounded if you do a whole house like this.
If you do your branch circuit at 110V AC and are behind a 15 amp breaker (still common in residential lighting to this day) you can theoretically run 220 6 watt LED bulbs. Which equals about 1320 watts of lighting. That is within NEC 80% limits and not beyond the scope of many households.
Lets be hyper-optimistic and say the same bulb only uses 3 watts if DC conversion is not done in the bulb. White LEDs seem to prefer 3.4V DC. So to get this same 1320 watt branch circuit, you would need cabling to support a 388 amp load, which is very thick and expensive, even if going with aluminum.
This is the reason that commercial lighting goes the
other way and ramps up voltage, to save on transmission losses, and minimize branch circuit complexity. I realize it is probably overkill in a residence, but just to help you see why your idea is bad.
Carmakers have wanted to bump up voltage in cars for this very reason, they are tired of spending extra money to provide several hundred amps to a car when they could be spending less for smaller wires at the same power rating.
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