Why would governments use a blockchain to enact fiat? Why would they just not print it at random as they have always done? It is easier, they know how that system works, and there is no advantage to them to put it on a blockchain.
Blockchain advantages in cost reduction
There is absolutely no scenario under which a centralized blockchain implementation can be a cost reduction over a database.
Exactly!
I disagree.
Right now the actual calculation of how many dollars exist is... Well, convoluted would be a compliment. With blockchain technology, the creation and distribution of the currency is reduced to a common protocol that all the banks can use for the price of a few servers. By comparison to just the regulatory compliance softwares in banks, that's a pittance. Whether they'll have the brains and balls to actually do it is another story, but the public ledger/blockchain idea for transmission of data and tracking the money supply would simplify really a lot of modern finance.