I do not see the essence of central banks in the bitcoin and blockchain technology. Bitcoin is decentralised and that is a good part of it. Getting a central bank for bitcoin means bitcoin owners will no longer remain anonymous.
The application of bitcoin in a country must have rules from the central bank, because the central bank is a rule maker in each country. Even though eventually Bitcoin is no longer anonymous. But for the long term, of course there will be binding agreements in each country, about digital currencies. Without rules, bitcoin will not be accepted in all countries. Only in certain countries, bitcoin can be accepted.