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.
Bitcoin has potential to become a global currency but their are many thing which creat problems for bitcoin to become a global currency. First of all it is a decentralised digital currency which means it doesn't under control of any kind of authority or government. And some government doesn't like this criteria of bitcoin. Bitcoin user does not pay tax to their government because of its digital nature and this is one of the main reasons behind this topic. It is highly volatile in nature and it does not has a strong base. So these thing stop bitcoin to become a global currency.