BTC lacks intrinsic value, people might falsely argue, sending transactions is the intrinsic value of BTC. Sending transactions doesn't give an edge for BTC to compete against traditional currencies. Until BTC doesn't have intrinsic value, replacing fiat would be difficult. One scenario where bitcoin would work as currency is when the global population, consider it acceptable similar to cowrie shells accepted by the people of Uganda.
Some of governments recognize Bitcoin as an asset, not a currency. It is something like a share of a company that can be bought without using a stock market and securely transferred using a strong asymmetric cryptography directly to a buyer which can live anywhere. I think the replacing a fiat money is almost impossible, because the national economies are based on them. The governments will protect the financial system of a country they managed. Yes, the shape of money is changing, the currencies evolve and go forward.