It's worth noting that the BRICS currency basically sounds like the Bancor idea that Keynes proposed https://en.wikipedia.org/wiki/Bancor

It's not a general currency, but rather one meant specifically as a clearing system for settling transactions in international trade. The main problem it solves is convertibility. Using a common currency allows selling goods to one nation, and then using the funds to pay another nation for goods you might want to purchase from them seamlessly.