There can be two cases. One is that all countries decide to go on a same cryptocurrency while the other case is that all countries bring up their own currencies for this matter. If we have the second option then the world would more or less be same but with much less black money and corruption because all transactions would be available to common people. Moreover if countries would themselves control the currency then more or less it would become centralized and not like bitcoin. But in the first case it would be pretty interesting. Because one currency would mean a much more connected economy world would become a global village without the bar of currency. Moreover the gaps between purchasing power parity of countries would also improve pretty much.