Would additional low voltage DC sockets be practical on mass scale?
I see the point, because you don't really want to convert from 110VAC/220VAC down to (say) 5VDC for USB, or 15VDC for laptops etc.

The problem is that for a given power as you drop the voltage the current goes up, which means you need thicker wires and lose more in resistive heating. However, there might be an argument for a secondary "ring main" in each house for (LED) lighting and electronics. Maybe 12VDC would be suitable. At 20A that's 240W which is quite generous just for lights, TV and laptops