For me, fiat is irreplaceable. Even in this modern or techy world, dont forget that, not everyone has the knowledge in using cryptocurrencies, especially the old ones, they prefer to use fiat than those digital ones.
At this moment, fiat unreplaceable because not many people understand about cryptocurrency. Beside that, crypto mass adoption is on early stage. I am believe if adoption become common in our daily life, people will start using crypto for payment because more secure