Actually if you had built it and it really worked on the plug&play level I think it would sell itself.. Don't make the classic mistake of thinking demand has to come before production. I bet if you could build a working prototype and give kickstarter type funding a shot you'd get enough money that could get you going.
I totally could, other than it's just a matter of focus. I've got other good projects going on at the same time.
I am also convinced it is ultimately merely a software solution. There is already good hardware that meets nearly all of these existing needs, namely, obsolete cell phones that people throw away every day. I don't understand why we endeavor to invent this as a new piece of hardware, when someone could go take a Motorola Razr, disable the cellular radio, retrofit it for this purpose with new firmware, use its camera to read QR and use bluetooth keyboard emulation as the output, put it in a box, and ship it.