To replace the dollar with bitcoin in the near future seems impossible, we all know that if the USA government is angry it will do everything possible to destroy bitcoin. I think it would be difficult to replace the dollar as long as there is no strong country that legalize bitcoin.
I don't think that bitcoin will replace dollar completley, there are people that don't like technology and don't have any mobile, and these people never will change to bitcoin. I think fiat money will be accepted always.