Powerline Ethernet is directly equivalent to littering in the park. By using it you are littering and being a jerk, even if you don't realize it. The FCC only tests such setups in very limited contrived ways. When it comes to actual house wiring the copper wiring is never impedance controlled, constantly approaches and leaves large metal objects, etc, so that it is always radiating radio waves. And powerline ethernet is HF (<30MHz) frequencies so those radio waves travel around the entire earth, ruining a shared medium. Just like littering in a public park is ruining a shared medium.