Honestly, any ODFM system is so incredibly resilient they will work over nearly any medium. I've tested powerline ethernet airgapped, and it still faster than the WiFI on the embedded system I was testing.
And that is the problem with Ethernet over Powerline. Because the power lines are not balanced or shielded, most of the RF energy escapes and can cause serious interference to licensed radio services.
And of course, if the interference can get out, it can also get in. Which is why Powerline Ethernet can work just fine one day, then suddenly stop working.
Plus the big problem with any ODFM system is that it is incredibly intolerant of wideband interference, eg a series of sparks. The reason being that the band of ODFM channels are fed straight into an A/D converter without channel filters. So each time that wideband interference takes out the system, the modem has to stop and renegotiate each channel from the start.
To any experienced RF engineer, Ethernet over Powerline (or any ADSL system) is a disaster waiting to happen.