The possibility of Bitcoin to be the only one world global currency is extreme and far-fetched. Every country in the world has its own economic setup dictating its own currency. The very nature of Bitcoints to be a decentralized crypto-currency goes against the acceptance as one global currency by the individual governments. To govern a country, they will not naturally accept the decentralized economic freedom offered by BTC and rule out the technology and the capacity for innovations. Even though it has been accepted by a few first world countries in their payment system, there are far more third world countries who need to constantly fight for existence. Hence, BTC is still not accepted there.

Even, in the level of micro transactions it is even more difficult as we can't wait for hours to get confirmation when paying in coffee shop with bitcoin. This concept didn’t really exist before. Presently, it acts more like store of wealth like gold right now. At this level what is required is faster confirmation and less fee might be used as suitable payment method for micro transactions. The pricing in Bitcoin is still too unstable, like any other crypto currency. Hence, to replace dollar we will need a currency that will have a much more stable exchange rate.

The way we cannot believe all humans of the world regardless of religion, race, creed or color to be able to live in perfect harmony with one government that represents the interests of all people equally. Similarly, it is still impossible to believe in the one world global economy (BTC) to replace every individual economic setup.

Let me disagree with you. Bitcoin or any other crypto cannot ever replace dollar and fiat money. No one country will agree to destroy its banks’ system and forget about USD, Euro, Pounds, etc. Fiat money and virtual currency however can coexist.