The question would be, how does the current money convert to the new money. If they convert after the current USD crashes, then those with debt in the old system would be in great shape and those with savings in USD would be screwed. Stocks wouldn't matter much since they would just reprice in the new currency. Bonds would be wiped out unless they have a clause that converts to a new currency.
What about credit cards, bank loans, and mortgages? Are they tied to the current currency or does the fine print allow the lenders to revalue in a new currency? Would they be able to force payment in the new currency?