The second stage to popularize cryptocurrency is to introduce it into the life of an ordinary person. So that everyone stops crying that their coins are worthless, they are used and then the demand for the purchase of currency will grow and the price of coins will not fall.
Yup, this would be a great option to ensure the fear against cryptocurrencies is gone. But the problem is, if the government makes acceptance a law, I guess they would do it with one particular coin, a single coin, might be stable or the value will be same as of the country-specific fiat. So technically, even then many cryptocurrencies would be invalid unless we have an option to trade other coins with the accepted coin or vice-versa.