I'm thinking to mesh broadcasting of cryptos  since a while.... your idea seems a special case for that... Till now I have thought of 3 major problems:

1) regulations... EM spectrum it's not availabale, best frequencies are already used and anyway subjected to licensing all almost all over the world
2) long-reaching frequencies (lowest ones) need bigger antennas, so you have a tradeoff between distance of relaying nodes and the possibility to install them or make them mobile and concealable
3) scalability problems of mesh networks... they work good when they are crowded, and noone is contributing to/using them if they don't work effectively

the only BTC-over-RF global project I know is Blockstream-SAT: that's cool and useful for sure for digital-divide zones, but the internet-to-sat supply chain constitutes a point of centralization