Of course, bitcoin can be a global currency if most of the country accept it. Wherever most of the country prohibited bitcoin, so it is very hard to be a global currency.
There are things which are not in favor of the bitcoins for now but we cannot say that things will never change. Bitcoin has a very much strong potential of becoming the global currency and that it can lead the world in much better way than any other normal currency. The only thing which we need to do is to wait for the time when things happen in a way like this and that before that, we must go for investing in the bitcoins for our better future.