Wont be happening unless these government will allow it to happen but i doubt,because any government who doesnt get taxes from the people wont survive there will a chaos and messy governance among the commong people.So it will be worst than we can ever imagine,that is why we still needs governments to protect ourselves from the people itself.
There are also governments which accept crypto usage in their countries.
There is still demand of fiat in third-world countries. I guess it will take a very long time for crypto to overcome fiat usage.