Nah it won't replace the dollar or any other currency... what bitcoin can do is replace the way inter country
forex is done... I.E instead of a country having to deal with all sorts of forex like GBP YEN USD ZAR RMB etc etc
they can just trade against BTC... currency stays in the country of origin and bitcoins move between countries...
so to speak.

it wont replace FIAT its not supposed to is supposed to regulate FIAT and the best way is inter country transfers.
countries who are self sustaining would need less bitcoins to trade with the world. Less demand for bitcoins is a specific
country the lower the FIAT of the country to BTC ratio i.e stronger FIAT currency so on and so forth.