Agreed, Btc can't be a global currency 'cuz price is very unstable.
It should be changing slowly then others can catchup it
fluctuation and instability of bitcoin is not a big issue at all, bitcoin is even now is almost near to become global currency, now bitcoin investors are present throughout the world, this is such a great truth that even those countries who have considered bitcoin as illegal now they are willing to turn bitcoin legal because they get to know bitcoin is need of the day and it is important to make our economy well and good.
Yes very true, bitcoin is now already present in all over the world may be very few counties will be there where the concept bitcoin still not reach and where people are not using bitcoin, otherwise i can see that in current time you can find bitcoin users in all over the world. Bitcoin is in fact the need of the modern time where we can expect that all the people will be using bitcoin for everything, and they will be giving preference to bitcoin over fiat currency.