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.
Yeah, seems like we're running a huge global experiment here.