The people in my country are already using their local currency and do not use US for their use but only for international use and when they will know about bitcoin the definitely they will replace USD with bitcoin.
in my country people have always used the official currency and nothing else, though it would be better if they used bitcoins
It wouldn't be better for banks tho, so that'll be the prime reason for not using bitcoin, untill banks find out a way to make a nice profit from implementing btc.