I think it is very difficult for digital currency to completely realize the idea of replacing cash, because each country's policy is different, which makes it difficult to implement cryptocurrency!
If we are going to talk for the whole world, probably it is not ready for cryptocurrecy. Because other countries did not adopt the uses of cryptocurrecy, they prefer to use fiat money. Some countries banned the uses of cryptocurrecy like bitcoin. However there are many countries are now using digital money or cryptocurrecy.