This does not work. Imagine somebody buys a coffee and he points the remainder to an exchange. As soon as the exchange “credits” him withthe funds, he buys funds in another crypto and “leaves” the system. Then he double spends the original funds and everybody but him looses.

The ability to “leave the ecosystem” prevents such a mechanism to be effective.

We have thought about these kind of things as well.

If you would have a crypto that does not allows you to “leave the ecosystem”, then proof-of-burn would work but such a crypto would be useless as you could never buy any real world assets with it.