I don't think bitcoin will become a world currency, at least in the short term. We all know that bitcoins can be used as a way of payment, but Fiat is still the mainstream way of the world, and it's hard to get a share in the payment field without the support of national policy.
Yeah you have a point. I think it is impossible because as we nowadays money is also one of the identity of a country. Every cointry has different currency so it is really possible that bitcoin can be the currency of the world.