I think the belief is that once enough parties shun the US/USD that because they don't trust each other's currency that they'll ultimately settle on Bitcoin.

Two things has to happen though. 1) BRICS has to get a critical mass of countries that, as a collective, move the needle significantly and that there is enough power to stand up to the US as a collective and 2) Bitcoin's price needs to appreciate enough to make settlement easier without the need for hundreds/thousands of BTC.