I’m not sure how that’s going to play out.
What will happen is that anyone doing business in Brazil or Argentina that wants to use this currency will have to sell Reals or Pesos in exchange. This devaluation will crush their sovereign currencies which is all their government central banks have the ability to create. Loans in the “South” will have to be repaid with Souths and, as Reals/Pesos are sold for exchange, the central banks will print more and more of them leading to hyperinflation and economic collapse.
From the standpoint of Marxists governments this will be a good thing since they hate private property and they can step in an nationalize whatever is left in the rubble that has value. This will happen as sure as the sun rises if they go ahead with it.