The reason for having reserves in another currencies is for your country to be able to buy stuff with that other currency from other countries, it is therefore

The reason for having reserves in another currencies is for your country to be able to buy stuff with that other currency from other countries, it is therefore an enabler of international trade. You seem to be seeing reserve currency as some sort of external piggy bank/store of wealth for central banks, which it is not. The only way what you are proposing makes any sense is when every country starts accepting bitcoin as the defacto currency for payment in international trade, which would never happen. If for example Japan wants to buy stuff from America, they'll need dollars, so they buy dollars with yen on currency as markets, why would anybody first want to buy a volatile crypto to, after which they still would need to buy dollars to actually purchase the American goods? Or should we replace all national currencies with bitcoin or something? What are you proposing? This has been the recurring problem with cryptofanatics, you understand nothing of basic aconomics and just spout this kind of nonsense which after a first uninformed look seems vaguely credible and you start convincing yourself that crypto's have any real use