It won't and it will never be a global currency. Imagine if the poorer countries wouldn't be able to adapt the technology due to lack of knowledge into it and I don't think that every single government would be into it since it is like a gonna be like a violation to themselves to allow something that is decentralized. They will keep encouraging everyone to not invest in here by posing warnings of instability of Bitcoin. It should just pose as alternative currency not the main one. People aren't supposed to be that exaggerated or greedy to the potentials it can offer.