There's no physical reason that power and signal can't share lines. Any particular device or protocol might fail to implement that, but PLC and even POTS show that it's possible and not even new.
The principle of power and signal separation has been used to send multiple signals over a wire since the duplex telegraph in 1872. It's one of the few things in this world older than the headphone jack standard that we've been using since 1878.
You may be surprised when you stick a multimeter into a standard POTS jack and read 48V. (Admittedly, the voltage is lower when the line is in use, but it's still there, which is why old-fashioned phones don't need separate power cords.)