I think it might happen, but the problem is "does the government in a country want to accept Crypto to replace a country's symbol, which is to replace currency"?. I think that is the problem that Crypto Btc and Ethereum cannot replace a country's Fiat currency.
That's a very difficult thing to replace because it still needs special negotiations by all parties involved in the government in a country, because every country also has laws that have been written neatly and have also been implemented by all of its residents, so when there is a change or mutations in finance, then this will cause confusion in rural communities who are not familiar with Bitcoin and Ethereum.