Of course, Bitcoin can be a world currency. However, Bitcoin is not valid in all countries. But seeing the popularity of Bitcoin,it will be the world currency for a time.Only the bitcoin has been known in all the countries, which could not make any other coins.Everywhere they are Bitcoin,world Currency Will be.
well bitcoin already become global currency but not every one accept it yet there is a value and you can use it to purchase something in every where( as long as they accept bitcoin payment). I do see people sell apartment and accepting bitcoin and also there is someone buying bmw and lambo using bitcoin. Maybe in the future bitcoin will fully recognized as currency.