We are now communicating on a way more advanced blockchain, than BTC. Central banks would never use Bitcoin as a base for anything but market manipulation.
When ECB can just type in whichever number of investment bank-currency, why in earth would they use a foolproof ledger system? It is so weird, how people don't know how money works, but talk about it all the time.
Because there will likely be some universal settlement layer in the future, especially after it is a race to the bottom in terms of central bank fiat currency money printing. Why would another country want to use something that the other country has an inherent advantage in creating? It's simple, they won't. There needs to be some universal standard, and as it stands right now bitcoin is the most likely candidate at this point in time. Doesn't mean it will play out that way, but there is a non zero chance it is bitcoin, and whatever those odds are, they are higher for bitcoin than anything else that exists at this point in time.