what would be wrong with creating the number of nubits equal to the amount of dollars available? Offer them for USD, make some rule they’re only used for the sellbuywalls, or some trickery, people use their NuBits happily ever after, maybe just half of the amount of usd if you think they will be around next to each other for a while still
probably a lot im missing here
i just imagined about this a little bit, maybe someone can explain that it is not really a good idea 
All told, anyone looking for all of the U.S. dollars in the world in July 2013 could expect to find approximately $10.5 trillion in existence,
using the M2 money supply definition. If you just want to count actual
notes and coins, there are about U.S. $1.2 trillion floating around the
globe.