bitcoin can't replace the dollar until people stop exchanging their bitcoin into dollars
Even if people will stop exchanging, some compare system will be needed for bitcoin anyway. Bitcoin can't really replace dollar anyway and it's true.
Yeah you are right replacing dollar by bitcoin is really not possible, but for bitcoin there is chances that it become a global currency and dollar come back to its home land USA, but dollar will still remain there.
It will not replace soon and of course you see that the value is rising slowly of Bitcoin and that more people is using Bitcoin now and that is of course good for the currency itself.
But there are still a lot of people that is using Dollar and dont even know how Bitcoin works and that is the problem.