Until this moment there is no cryptocurrency that I know off can replace Fiat or overcome the use of Fiat, Bitcoin and Ethereum are near but still a long way to achieve this. Currently, in trade, a lot of people with a goal of increase Ethereum and Bitcoin and this is one step in the right direction but those same traders will then convert their holdings from Ethereum and Bitcoin once they have the chance to do so to Fiat, you can notice here Fiat is the ultimate goal for most people.