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I'm pretty sure that there has been previous attempts at this as well, like sending BTC via SMS or some form of transponder that doesn't utilise 3G.
Personally I don't think that these will be significantly used in the future given the widespread use of the internet, even in remote regions now. But these non-internet based developments could certainly be useful as a backup for if somehow the electricity grid completely fails (unlikely to begin with), or potentially, sending BTC in space.
Exactly. And that still requires a degree of trust given that both the sender and receiver can take out coins from the address at any time, and accuse the other of fraud. That's the thing that needs refining, as well as the security aspect of brainwallets.