There are already a couple of ideias following this topic's subject.
I believe last year they a couple of them were already made but in a eletronic way where you would use them in some machine and use their linked addresses to receive and store funds.
I too came to know about it with the QR code being printed on the currency. I'm not sure about the same. I came across coins which carry our wallet address, this is provided through the goods and services section with universal shipping access. It resembles a coin with bitcoin symbol and wallet address molded to it. More users preferred it for gifting. There isn't any big usage same might be with currency as well.