BRICS note is never going to be a real thing.
Fiat money is everything about trust, and BRICS countries don't trust each other at that level.
PS: backed partially by gold is an illusion, as it also has to be trusted, as it's not possible to verify it.
Regarding trust between the BRICS countries:
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What prevents them to print more paper than gold?
Exactly.
That's why that "gold backed money" would be just like any other fiat money.