The best-selling financial book writer "Rich Dad, Poor Dad" said Bitcoin would replace the US dollar, which he called "counterfeit money." In the April Sane Crypto podcast, author Robert Kiyosaki said the practice of printing more money in America was to create bubbles that would explode. "I think the dollar is toast because gold and silver and cyber currencies will take it," he said. "The US dollar is a fraud. I think we are watching the end of the dollar. "
https://www.youtube.com/watch?v=unvFvAUCZEUIt will be not that bad after all but I am hardly doubting in that, cryptocurrency is still so young and not trusted from the side of government so I am really the hard to believe in that prediction.
I agree cryptocurrencies are still newbies to the financial world even they posses many feature and qualities than fiat currencies so even above predictions are accurate it might take considerable amount of time for that to happen because unlike cryptocurrencies major fiat currencies are run by most powerful governments in the world example for USD and GBP so will those government let cryptocurrencies to take over the world without a fight I doubt that so it will take much time for that to become a reality