I have less information about abroad but i must say something that we have to reason collectively,
Out of
195 countries in the world i know too well that most of the population (country's) are solely depending on USD, EURO, POUNDS, YUAN for major trade. I mean before anyone could trade among these 195 you need any of those currency to be able to travel across, and if only 6 countries decides to breakout from USD how do you think it will affect the US dollar?
There will be no much effects
The USD accounted for about 60-70% of international transaction in the global economy (let's say 65%). Now BRICS accounted for about 23% of the Global economy, current BRICS countries estimates 85% of their
transations in USD. If all of this will be converted to a new BRICS recommended currency(assuming 85% is equivalent to the economy meaning economy=international transactions) So 23% multiply by 85% equals
20%. So this 20% will be taking out in the 65%, I mentioned earlier. USD will be left use by 45% only now BRICS still holds the 23%. Going back to your statement "Noeffect", thats 1/3 of the USD used transactions.
But wait theres more, there are some countries have the intention to join BRICS, even Euro like France consider settling some trades with China in Yuan. And dont get me started in the Middle East. SEA, South America?
Please correct me if Im wrong.