I have been working on this area for 2 years now and created AirMount https://www.airmountapp.com. You don’t need the cloud, internet, Bluetooth or USB. Today it works between iOS and Mac, and now we are building it out for Windows and Android. I dream of the day when sharing files with any nearby device will just work like AirMount does today, irrespective of their OS. The industry needs to collaborate to make open standards, but in the meantime I intend to push the limits of what is possible already.