The fiduciary money will disappear sooner or later, so the cryptocurrencies should not improve the fiduciary money, since its mission is to replace it.
Cryptocurrencies not only lower costs in transactions, they would save money production costs both in bills and in currency.
To fight against this is to fight against the inevitable.
Also today a large percentage of the money we use is virtual, since they are only numbers in our bank accounts.
RE: Central Bank Issued Digital Currency Will Not Improve Monetary Policy