that's a difference to appreciate: settlement currency vs. consumer currency.

they have repeatedly said they won't introduce a common consumer currency, like the Euro for the EU is, as BRICS is all about maintaining the sovereignty of each member country and the Euro is all about slicing that sovereignty away for EU countries.

But a currency to settle trade flows is something altogether different; as you say, it's a way to regulate the cash imbalances created by trade flow. People ould never see it.

If I'd bet on it, I'd bet on a BANCOR-variant for this, as was proposed after the second world war (but never happened, because the US said, ha, no, that's way too equal, be my colony instead). That wouldn't come with a need to transfer physical gold, though it could be backed by gold or, more likely, a basket of commodities these countries all have among themselves (again, a basket would equalize things, as the imbalances in gold ownership and/or mining in these countries couldn't skew the power relationship all that much). Bitcoin, of course, would be a commodity that everyone can access equally regardless of the whims of mineral deposit fate. ANd it would make for easy transfer for regular balancing.