In my opinion, no cryptocurrency can replace national currency. Even bitcoin cannot replace any national currency. Why? The prices of these cryptocurrencies are determined based on this national currency. What would be the value of bitcoin if not made as an equivalence of the USD? It is these national currencies that gives bitcoin and other currencies their value. I see Crytocurrencies as an asset that we buy with national currencies and so its hell impossible to replace fiat. Bitcoin will live for a long time but only with national currencies.