Probably the reason they aren't saying much is it is still being figured out how it would work. Here's the framework:

BRICS Contingent Reserve Arrangement https://en.wikipedia.org/wiki/BRICS_Contingent_Reserve_Arrangement

From what I can tell it is mean to work along the lines of the Chiang Mai Initiative.

Chiang Mai Initiative https://en.wikipedia.org/wiki/Chiang_Mai_Initiative

But now there is China and South Africa wanting to expand to include others, and Russia and India wanting to not expand. So they got things to work out yet it seems.

But unlike IMF's SDR which are issued by the IMF, this R5 (or now, R5+) is just a reserve pool allocation, not a currency that is issued.

But there's no info I've seen (from casual search) that says how this would work as far as allocation. If South Africa is supposed to kick in enough rand to have an allocation of like 10% of the reserve pool, what happens when their exchange rate increases or decreases? Would they have to kick in more, if the rand loses value? And how often is that rebalancing occurring? etc., etc.,

It will be interesting. Not a single one of these are publicly discussing how bitcoin fits in. They want to move away from the dollar, that I get. But if these emerging market currencies get decimated because of bitcoin, the BRICS / R5+ becomes more greatly tied to China's currency.