It can be, because bitcoin has the potential to become one, but this thing will take place in a matters of years because as for now many countries have not yet recognize and accept bitcoin. For bitcoin to become world's currency it has to be accepted universally and become one world currency.
I do not think that bitcoin could become first world currency because every country has their own currency and not all country accepted bitcoin. It could possibly used for payment online everywhere for online shops but cannot be used as world currency because there are regulations in the government that we have to follow.