Excellent, as an American I wish them all the luck in setting up an alternative currency standard.

The US has been hurt by the 'exorbitant privilege' of having its currency be an international reserve standard. Dollars that pile up on balance sheets and central banks' books get recycled into US assets and debt. This is part of the dynamic that drives the trade imbalance, which (on net) imports unemployment into the US, via lack of competitiveness.

Yes, the dollar would drop in value if the world's banks used a basket of currencies instead of large, dollar-denominated holdings (often T-bills). And that would be good for the US.