I think cashu and others are doing something like this. I’m not 100% up to date on the topic, but I remember hearing about the ability to do similar things with paper redeemable through mints. I probably should do more learning in this subject.
Discussion
Also interesting. I’ll have to research that too. For a paper currency to work, the value of the note must lie in the authenticity of the very note you’re holding, rather than any information on it that can be copied, so a paper qr or something doesn’t fit the description.