As long as the US remains the superpower, both politically and economically, the dominant of US dollar in the world market will persist. It is less likely a change in the foreseeable future.
In Europe, we have euro but British pound and Swiss franc stay. Some big countries are just reluctant to abandon their own currencies because of their own vested interest or supremacy.
A single currency takes decades to establish. Not a worry to forex traders. :cheesy: