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.
You got the idea why it will not be called as the global currency since not of all thr countries around the world are opem to acquire this currency and be used as daily basis of life if a simple transaction will only cause a medium or cash to be able to perform successfully and I guess we are not responsible for forcing people to acquire Bitcoin if they dont really want.