If every nation adopts cashless system, bitcoin will surely be the currency of the future days. The reason is that no other digital currency has got acceptance and popularity similar to bitcoin though lots of digital currencies have got existed.
Every Nation will diffidently adopt cashless economy in near future as technology is changing very fast every day. Now goods are sold online and we pay through debit/credit card or through net banking so that day is not far when the world will be using Crypto currency. I think that day every nation will have their own digital crypto currency and world will forget the word FIAT.