You also have to take into consideration the availability of technology to be able to implement it as a worldwide currency... Anyone can have access to dollars because they can hold it in their hand, such as people in Africa. They cant hold bitcoin in their hand, because they need advanced technology, and people in Africa have little to no access to advanced technology as of right now. This is also the case in other LDCs (Less-Developed Countries). One might say it does not matter because LDCs don't really help the world economy, though. Its all a matter of opinion.