They seem to forget the whole reason the USA left the gold standard, which you mentioned with Charles De Gaulle. As a world reserve currency, there is so much debt outside of the Federal Reserve's control, such as the Eurodollar. The world was printing more dollars than the USA could back.
If the Gold BRIC were to gain traction, you'd likely see a EuroGB of some sort, which then could use to extract gold from those nations. However, as you mentioned, the USA alone could amass a sizable amount of their gold reserves just by normal commerce.
The Chinese could clean up. They are the world's #1 exporter meaning they would be pulling in a ton of the currency.
Xi simply turns around and says, give me the gold. It is a flaw when you make a currency asset backed instead of building the value on the currency.