The road to the Euro started with borderless movement. Then they got a governing body, followed by bureaucrats... a lot of bureaucrats. They built up a central bank, and made trade frictionless, and finally, after 54 years(1948 to 2002), they introduced the Euro. Everyone was shocked how quickly it happened.
The BRICS are not even at the beginning of the 54 year time scale. They have no bureaucrats, nor any governing body. They have no treaties. They meet once a year, but that is about it.
Their bilateral treaties are weak. Russia and China might have the strongest trade, but we have better trade with China than Russia does. India and China are in a near state of war. Brazil and South Africa are way out there, trading more with the USA and Europe than with anyone else.
There is no shared culture. The EU was a bunch of Europeans who had all fought with and against each other for over a thousand years. Even the enemies intermixed. The German/French border is full of mixed people. What is the shared culture between Brazil and India, or South Africa and China? Even the countries that have borders have nearly unpopulated borders, no intermixing. Russia's population centers are thousands of miles from China. China and India's border is virtually uninhabitable.
Not just no shared cultures, but cultures and economies famed for their independence.
What I am saying here is it would take 50 years for the BRICS to even get on the road to take 54 years to have a shared currency, and I might be too optimistic. The lack of a shared culture makes me think it might take a thousand years even to get to the 50 years...
Assuming I am not frozen for two thousand years, and the thawed out, I will not see it in my lifetime.