You did not mention the other way to create “Fiat-tokens”, and that is proof of burn. I am thinking about eUSD, a stable coin created by sending ETH to a provided eUSD smart contract. The burning process means that some eUSD are minted according to how much ETH at current market value is sent to a smart contract where it will be locked forever. That is a smart way to migrate crypto, in this case ETH into “fiat tokens”.