A good idea, except that there's currently no standard for indicating that a port is "for power draw only." If you go with the simplest device design, a simple Y adapter, consumers will get confused as to why they can't plug in two data devices.

Perhaps the solution is to create a plug/socket spec that only allows for power draw, and make one of the "female" ports on said Y adapter a power-only socket.

There's still a catch, though; AFAIK, USB devices are required to report how much current they use to the USB host, so that the host knows if it's capable of supporting the device. (If it's not capable of providing that much power, you get an error message asking that you plug in whatever device it is into a different port.) Break that functionality of the USB spec, and you can't really be assured of the reliability of that part of the USB network.

I don't know whether existing USB peripherals such as LED lamps and fans report that information, or if there's a provision in the USB spec that specifies an upper limit to unreported current draw.

AFAIK, those such appliances are "dumb" in that they only take power from the port.