It's interesting that even the cheap consumer grade Mavic drones have the ADSB receivers and will automatically warn and even avoid traffic, but many of the real airplanes won't.
It may sound drastic but think the FAA should require ADSB OUT and some form of ADSB IN with no exceptions. the aircraft without electrical systems can be extra dangerous since they often do not have a good radio (just a handheld) or a mod C transponder which would show up in the areas with the FIS-B coverage. They typically don't bother with the ADSB IN either.
the modern ADSB and GPS devices have very low power consumption and can be powered by a battery.
There was a recent fatal mid-air involving a CAP and a miscommunication (or lack of) with a non-ADSB plane. How can there be any debate on whether the ADSB can save lives.