I normally agree with counterarguments rooted in the state's monopoly on violence, but in this case other options for the PHY layer exist. Seamless multi-PHY i

I normally agree with counterarguments rooted in the state's monopoly on violence, but in this case other options for the PHY layer exist. Seamless multi-PHY is possible if care is taken to prevent leaks in the abstraction e.g. precise timing expectations up the stack. Plus, plenty of side channels exist with our conventional PHY. You can copy beacon frames from nearby 802.11 APs and rebroadcast them at just the right time to achieve transmission of an FSK modulated signal, for instance. (In this case there would just be more of the same beacon frames in the air. You'd have to look at what the AP advertises as its broadcast interval to know that they don't belong there. Furthermore, you wouldn't be able to easily pinpoint the source of the extra transmissions or decrypt their content under a well-designed protocol.)