Economic scenario discussions are valuable, but this one isn’t credible. If USD sustained a rapid 50% devaluation, I cannot imagine a situation where the causal event that lead to the decline would not also affect the rest of the World’s currencies.
If this day comes, Nu’s ability to respond will be important, but likely less important to each of us, individually, than trying to survive whatever social, financial, or civil cataclysm caused that immediate 50% devaluation.