SDR (Special drawing rights) will displace the dollar before the yuan does. SDRs are instruments created by the IMF that represent a basket of currencies held by IMF member countries.
The yuan currency market is too small and illiquid to displace the dollar as the world's reserve currency.
I doubt that SDR will ever replace the dollar. From wikipedia:
> Special drawing rights were created by the IMF in 1969 and were intended to be an asset held in foreign exchange reserves under the Bretton Woods system of fixed exchange rates. After the collapse of that system in the early 1970s the SDR has taken on a far less important role.[5] Acting as the unit of account for the IMF has been its primary purpose[Williamson 1] since 1972.
The yuan currency market is too small and illiquid to displace the dollar as the world's reserve currency.