It's a great topic of discussion. I am convinced that it is not. Bitcoin has every chance of becoming a world currency
Bitcoin have every feature required to be a World Currency, but every country won't take the similar stand. For now few countries have shown green flag and one have made it legal tender within the country. These are part of development. Bitcoin will serve as the alternate to fiat, because it is really tough task to eliminate the entire usage of fiat and implement crypto.
It's simply a matter of people to start accepting Bitcoin for goods and services, and then people starting to use Bitcoin to pay for those goods and services.
Simple as that.
If people keep simply buying and selling fiat for Bitcoin, then the demand for fiat will be the same, and the demand for Bitcoin won't increase.