I like the idea. I just wouldn't trust a device with any kind of connectivity. I guess recycling an old disabled smart phone (no wifi, no sim, no bluetooth) would be a good starting point. Maybe I should get the patent in now.
research "hardbit" your a bit late on the patent
and as for the inspiration for the idea.. although i brought it up in the other thread, it has been an idea being left idle for months, i see no purpose in any web wallet needing login's 2 factors and long entropy passwords.
all a webwallet needs to do is receive a signed TX from a client side script that forms the signed tx, where the online server never see's nor touches a privkey. but you are right simple QR code scanning is the easiest way