"Therefore his wealth would, in reality, be replaced by an equal 'value' of Crypto for the new economy"
That is likely wrong, because it would cause all (non crypto) markets to crash lets say 50% at least. It will create a lot of FUD and destroy wealth everywhere.

Remember when the EURO was created? They promised everyone would be better off, when in reality prices doubled and our money in the bank was cut in half. This was in fact a haircut by 75%. Everyone lost 75% of what they had before. No joke. And most people did not even realise this truth. They thought they lost only 50% but prices doubled within a month.

Whenever there is a transition in payment methods, people loose a lot of money by design. That's one big and easy way to steal from the many.

What I mean by fiat can be replaced anytime is, that if people loose trust in a currency and it gets literally worthless like we are seeing in venezuela, they will, after a short period of suffering, just try to introduce a new fiat currency that they can issue and control.

But this time will be different. Experts think that people will not accept another fiat currency. It would have to at least be backed by gold. Even a government issued currency might not satisfy the plebs this time. That's why cryptos are actually fighting for the next reserve currency status. It will not be bitcoin, because it is slow and expensive. But one of the fast, zero transaction cost currencies might be fit for this.

I think they would just issue interim arrangements for taxes and offer some fixed exchange rates for fiat debt.

Cheers,
@ew-and-patterns