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There are no current exist cryptocurrencies that could replace USD as a global payment, and if there is someday i'm sure it's hard to replace it because the power of the people who controlled the paper fiat money is too strong, they already ruled this world for many generations so i think it's quite imposibble to create an environment where everything is paid by cryptocurrency.
Keep in mind that there is a big difference between widespread usage and replacing.
I have always said that bitcoin is never going to replace fiat and it wasn't designed to do that either but I also believe that there will come a day when bitcoin can be used anywhere in the world. For example tourists would no longer need to exchange their fiat to their destination country's currency, they would just use bitcoin when travel.