The maximum numbers of bitcoin to be mined is 21 million bitcoins. Bitcoin can not be used as money by the whole world because it has a maximum cap. My opinion . What is your stand ?
Bitcoin has the liquidity so one bitcoin cn be divided into so many parts and it maybe enough to handle 7 Billion people of the world.But we don't have only bitcoin as the crypto currencies and other thousand more crypto currencies are also available so it can be enough to replace the fiat money system.
I'm a bit doubting if Fiat will really perish or even transformed into another form, the digital world is no doubt in its development but still cryptocurrencies run using electronic technology and it requires electricity to work, 2 things that can be dangerous if relying entirely on Cryptocurrencies.