As someone who had an electric train as a kid, I doubt that it would be practical to send 5Volts anywhere in the house and expect to have any output voltage at all by the time it got to the wall outlet. More likely we will be sending 120V (or higher) to each receptacle, which will have a wall wart built into the box at each outlet.
BTW, McDonalds looked into those receptacles in the picture and it's just another good idea that's 'not ready for prime time'.
