It won't work with how the world is arranged today. The whole point of the EU is to bring in new states and slowly bring them up to the economic level of everyone else. This process lasts years until the government is ready to switch over currencies, if they want to. More often than not, switching to the Euro has been a success.
For a global currency, all governments involved would need a level-er playing field. And if you want to involve certain parts of South America and Africa, it almost sounds like colonization all over again. Would have to see the plan, but it would take a heck of a plan for this to work. Don't see it happening in 100 years.