The shared currency would be "BRICS" because it would brick as much as the Brazilian currencies (yup, plural) in hyperinflation times. (I'm old enough to remember the river dolphin 100 cruzeiro coins).
Jokes aside, opinions in this regard that I've seen in Brazil are rather lukewarm to the idea. Most people whom I've talked with didn't even know about it; the ones that do might say that it's a bad/good idea, but I think that most people realise that it doesn't really matter much. Plus Lula has a tendency to speak about things that never come to fruition.