Considering what you are saying here, this isn’t a bad idea at all.
I would advise you to post this in a new post so that we can discuss this properly.
These are all correct so yes, there are a lotta considerations even if we can do this.
I do work on NFC cards so it is possible to make NFC cards very easily without the requirement of connecting it to a bank account for fiat. I mean, the fiat conversion could be done in a different way in the backend. I have seen it in a workshop at college how they make NFC cards and upload the firmware on it after which you can just Tap-n-Pay. It’s damn easy.
So there is definitely a way to do this in a completely decentralised manner as well.