The protocol isn’t even the issue, banks already use XRP.
It’s the fact that USD is propped up by Uncle Sam’s globalized monopoly which is kept in tip top shape by geopolitical power.
Everyone trades in USD because it’s the de facto currency and it’s stable because the government can abuse its power to keep it that way.
No one trusts the value of the Ruble, Yuan, Rupee, or even any other currency except for maybe the Euro. They all exist for internal use, which means its just gets compared in value to USD whenever you have to deal with anything external, which is all the time.
BRICS would only fly if a stable trade medium can rapidly prove its worth with market stress and trade requirement, otherwise everyone will just continue to use USD, hence why the USA doesn’t currently view it as much of a threat. And even if you could get countries on board, the US can hold on to a massive noose around everyone’s neck by refusing to trade in anything but USD, which would effectively shut you off from trading with a massive portion of US based/owned/partner companies.
From wikipedia:
The plot intro: