if there is a new world currency, the exchange rate that other currencies are converted into it will be a huge factor IMHO that will likely impact the price of everything else. personally in my opinion, i think the US dollar will get a lower buy-in price relative to currencies that hold US treasury debt. i think this may be offered as the solution if it is ever believed by monetary authorities that the US cannot repay its sovereign debt.
a new world currency would also mean the US dollar would lose its role as world reserve currency. this would sharply decrease the amount of savings held in US dollars, particularly outside of the US. this would also decrease the value of US dollars.
i focused on the US dollar here because that is the scenario i am most familiar with, but i think the basic theme will be that the insolvent a nation is, the more its currency will get devalued with the introduction of a world currency.
anyway, just my opinion.