That is sort of becoming a thing with USB outlets. It is starting to become quite ubiquitous. I wouldn't be surprised to see an outlet that had 4+ USB ports and a standard outlet maybe.
> Also, USB outlets still down convert 120V AC. It'd be much better to do it in bulk at once place in the house and let devices use that
That's not entirely clear. Low-voltage DC has higher transmission losses, so converting to USB-level voltage in one central location might do quite a bit worse. Plus, you still need logic at the plug to detect how much power to supply.
This is my opinion as one. Switching supplies are 90+ efficient, at nominal load and they are less efficient below and above that nominal load. So your 48VDC converter might by 87% efficient because its rated for 500W and you're only drawing 50. And your 5V regulator may be only 92% efficient while your device is charging but 88% when your device is 'idling'.
