it is not that easy to be a global currency because all aspects must be met if bitcoin want to be global currency, I think bitcoin is not yet deserved to be a global currency because many aspects that have not been fulfilled ..
which aspects you are talking about , it serves most of purpose of a currency .
we can store it , transfer it , utilize it as mode of payment , have a value (volatile though) . so it is already a currency , only thing is it is not legal in all countries . apart from it tell us why it can not be global currency ?
Same as you I really wonder why people keep on saying all this even if they have no proper logic behind it, as according to me bitcoin si gaining good attention of people worldwide, bitcoin is just like and good luck Cham in a lot of countries because bitcoin made then enlist of well developed countries because of its importance and highly benefits, now in the whole world almost everyone is satisfied with bitcoin so it will soon be the legal currency universally.