If the EU changes to BRICS or another system, the dollar is done and America becomes Argentina.
That's funny.
Why would the EU spend 50 years building a trading bloc and currency union, to then just throw it all in the bin and join some half baked upstart organization that is literally decades behind on that front?
The idea is to promote the use of the Euro over the dollar. But how?
There is always a lot of talk in Europe about how they are going to switch to paying for oil and gas imports only in Euros - for example. But that's not how the real world works. Why?
1) The guy that sends you the invoice, decides how he wants to get paid - 99% of the time. This is probably because their costs, debts, and accounting are already in USD. In addition to this, they likely don't want to deal with the currency exchange risk inherent when you get paid in euros, while your costs are in dollars.
2) All the global oil benchmarks are priced in dollars. Figuring out each and every day how much more or fewer euros you gotta send is a pain in the ass. Eventually you will start hedging that risk, and then you're back to where you started, and may as well have been using dollars all along.
So what you have to do, is to convince the Arabs, and the Russians, and the Angolans, and Algerians, etc that it is in their interests to get paid in Euros. For that - you will need at least a few decades of work.
To be interested in getting paid in Euros, you have to be interested in holding Euro assets. That's how the so called "Petrodollar" came to be. America paid the Arabs enormous amounts of dollars, and the Arabs promptly recycled them back into US Treasuries and US stocks (largely bank stocks). The dollars left the US, but only for a second, before coming right back.
There are not enough quality Euro assets to absorb the tens of trillions in demand for US assets that you seek to replace.
You don't have a singly stock market. Meanwhile, the US has the widest and deepest markets in the world. Next - the US owes the whole world a crazy amount of money (US Treasuries), whereas you kinda don't. First of all you don't print enough of that kind of debt, and second you owe it mostly to yourselves. Because the Germans are in charge of your Union - I don't think you'll ever get to those kinda levels.