The vampire voltage/phantom voltage use could be eliniminated by incorporating a switch into the USB socket that only turned on the USB when something was plugged into the USB.
I don't think that would help much (I as I think most people would do is just leave the USB cable plugged in all of the time and only unplug it from the USB device) Maybe a sensor to monitor to see if the device is actually charging/Drawing power would work but of course cost more
