...what changes would need to be made?
Cryptocurrencies are terribly unstable and volatile, how would this be addressed?
What other barriers may need addressing?
You would have to issue physical bitcoins backed by a reserve.
This is the only way to have bitcoins used for day to day transactions.
I think only a country with large surplus and substantial assets would be able to do this.
They can protect their citizens from volatility to a certain extent.
I don't think any country would do this by dumping their own fiat currency, which means they lose the authority of issuing cash and a method to adjusting the economy(print as many cash as they like to get rid of debt or enrich themselves). The reason is that the production of bitcoin is scheduled and the issued number of it is fixed, no any third party can control it.