in my opinion to replace the fiat currency is not possible because the legality of the crypto currency is not recognized by all countries in this world and they still believe in the fiat currency of course
We do not know anything about our future. Probably, the writers of science fiction were right, and robots will replace some people in the future. If it happens, the cryptocurrency can also replace fiat.
All possibilities are very large indeed. we cannot give an opinion whether it is true or not but from what is now that all is progressing and it is not impossible to happen