It could potentially hit the dollar, although only through secondary effects...
Mahmoud Ahmadinejad, president of Iran, urges Opec to consider pricing crude oil in other currencies.
Iran can invoice its oil customers in cowrie shells if it likes, but that would not change the underlying value of the product. Shifting oil markers to other currencies would only make for inefficient markets.
It could potentially hit the dollar, although only through secondary effects: by knocking confidence and spurring diversification of global foreign exchange holdings.