I mean.. once you have to start to buy specialized cables anyway, you might as well have specified in the PoE++[0] standard that only specialized PoE++ cables are accepted, verified by device handshake. And then you can engineer the whole thing to basically be "Powerline but with higher data rates", making the cable power-first instead of data-first.

[0]What a horrible naming. PoE 2, 3, 4 etc would have been much better..