Currently bitcoin doesn't affect the total world economy seeing that it's not generally accepted in all countries of the world. There are so much restrictions and ban the currency is facing in some countries and this policies determines a lot on how bitcoin could effectively affect their economies.
In my view I don't think bitcoin can completely replace the traditional currencies and that's because we have different governments in the world representing a country and their local currency being their element of pride they won't completely abandon for an international one. Even today we have some people that for no reason don't own a bank account, for they're just not interested in going digital with their financial transactions even though it's in fiat same with bitcoin not everyone would have interest in using it hence it can only complement with fiat as it gains more acceptance and usage giving humans a financial choice as it suits them.