I thought about this technology for bitcoin offline wallet. So like you'll get any mobile phone, install some bitcoin app, put it to aircraft mode (or even destroy all wireless chips if you can do that). Or just laptop. Then you'd use it to generate wallet, sign transaction and then QR this transaction and receive it via another phone which is connected to the internet. So private key is never leaving offline device and all communication with the outside world is through human-eye controllable channel. Should be impossible to compromise using digital methods (assuming that wallet application is trustworthy).