My gripe with this is that people seem to take this as a fact that hasn't even occurred with almost 100% certainty that it will happen.
A lot can go wrong in 20 years. So far, all economies that challenged US in the past mysteriously gets IMF'd, pulling the rug out of a credit bubble that they help create by twisting the arms of the central banks that are supposed to be free from this kind of interference:
This documentary about Japanese central bank is eye opening to just how much grip the US hegemony has, one which I fail to see China being able to emulate anytime soon because of the hostage situation that US allies are finding themselves in.
https://www.youtube.com/watch?v=p5Ac7ap_MAY
The theory that states Sadam was whacked because he started to accept euro instead of the petrodollar standard makes an awful lot of sense.