As far as I understand, and I have no formal education, all of your questions are the same question…

Well, there are some assumptions to be made:

1. Bitcoin will achieve hyperbitcoinization.

2. This will lead to Bitcoin having a stable purchasing power.

In this case I don’t see why we would need other currencies. When a local economy expands and as a reaction the local central bank inflates the money supply, people will flock to Bitcoin, rendering the central banks monetary policy useless.

What am I missing?