The author of this article has done a simple analysis of why cryptocurrencies will eventually replace fiat currencies.
Whether or not cryptocurrencies will replace fiat currencies depends on many factors, many of which have not been addressed by this author. Factors like the economy, government intervention, illegal activities facilitated by cryptocurrencies, issuance and control of supply, valuation and more will have a bearing on whether crypto will eventually replace fiat.
Subash Chandra Garg, an Economic and Finance Policy Strategist from India took an opposing view to the author of this article in his blog post dated January 02, 2020, which can be read here: https://subhashchandragarg.blogspot.com/2020/01/currencies-will-be-digital-crypto.html.
He took an extreme position by stating that crypto will not even survive, let alone replace fiat. He listed three reasons for his stand. His arguments gave me the impression that he has not got his feet fully wet in the cryptocurrency market yet.