I would find this super cool if it wasnt for the fact that all of the radio frequencies are owned by the military and corporations. Outdoor IoT could be amazing, but it is kind of dead because you cant actually connect it to the internet without laying down cable or using 4G which is horrible for low power applications.
I don't know what kind of idea you are getting. Radio and wi-ifi are waves. The wave is what can be used, you don't care who generated it. To say it somehow the wave is in the air and you just take advantage of it being there to convert it to energy. Doesn't matter what the wave could have been read as. In general a radio station is not going to stop working for a whole region just to stop you from using it.
Anything that can be powered by this research, can also be powered by a button sized battery for weeks if not not longer. I thinks its more intended for very off grid stuff but maybe im just too uncreative.
There are already lots of concepts for low power wireless communication for example LoRaWAN
The issue is not the ISP its the technology used to establish a connection between devices. We need hardware that can run with the low power requirements that come with this research.
That's not any sort of legal issue stopping you, that's physics. If you're trying to create say, some sort of mesh network, and the device is using all of the signal's power just to run itself, there's no power left to retransmit. You don't get something from nothing. We're talking microamps and smaller with these devices.
If you've ever used a crystal radio, you can get an idea for how weakly powered stuff like this is.
Edit: look up the channel "EEVBlog" on YouTube, dude has a dozen videos on various such devices and goes into the actual math and viability of each.
Technically, a properly tuned receiver that's using the signal for power can create radio "shadows" behind the device. People have also been caught with giant coils in their attic siphoning power from nearby radio stations and high voltage power lines, because they can detect the power draw.