It is not realistic that cryptocurrencies will replace fiat currencies, at least in the nearest future. Nowadays most people around the world are using the fiat money and also banks support mainly fiat and fighting cryptocurrencies. So it will take many years at least until crypto can replacing fiat.

Cryptocurrency to replace fiat will not be very easy at all. I like to trade more with fiat currencies than cryptocurrencies. I do invest in cryptocurrencies with the aim to claim more interest at the end.

For that to try and occur, everybody must have a handheld gadget or a financial framework to do trades. Everyone additionally should have a web association somehow to do their exchanges and that could be a test since the web itself has been with us for 10 years or two and you can't have a web association all over the place.

I think Fiat will still be using it a lot because Fiat is a currency that is easy to use and does not need electronics to use it because there are many parents who do not understand technology and of course cryptocurrency will not be able to change Fiat.

this is the most possible outcome

Eliminating fiat is the worst thing that would possibly happen since almost all people were aquainted on fiat.Digital currency could give threats on the governments governance because they cannot possibly control on how people used their digital money.

Fiat is known by all people and it is also used by all of the people in this world that's why crypto will really need many years before they can replace it, but if cryptocurrency will continue to grow very well, there is no doubt that the chance to replace fiat will increase.

Well yes, as you said, they could track you down if you were using a centralized cryptocurrency, or if whatever crypto wallet/exchange you're using requires you to be transparent about who you are. Such a situation could also make it easier to control exactly what you can and cannot purchase, where, when, and why. You can already be blacklisted from banks and using cards, ATMs, etc, but if everything was crypto, it seems like that would have the ability to take it up to a whole new level. The Bible even talks about a one world system where you cannot buy or sell without basically selling your soul to get a special mark - not good (see Revelation 13:15-18, 14:9-13).

It's probably best to have OPTIONS, a little crypto, some fiat, precious metals, etc.

Just recently watched a video about the history of the world's current fiat system, and how every country is currently on fiat, which is not looking good. The thought crossed my mind that crypto is kind of coming right at the time when a new money system is going to be needed. Here's that video:

140 Years Of Monetary History In 10 Minutes - Mike Maloney   
https://youtu.be/wD3KYlpE2lk

Cyberius

This has not been a simple undertaking at all and can't be on the grounds that we are generally anxious of such change and furthermore the intricate idea of utilizing cryptographic money is another extraordinary impediment for individuals to move into digital currency. On the off chance that we can make cryptographic money use simple and on a solitary platform,everything should be possible with speed,we will progressively win this battle.But for the time being regardless we have to accomplish more before we can supplant fiat with digital money.