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.
It is true that bitcoin cannot replace dollar but it is not correct that for bitcoin as a standard to be compared with dollar is compulsory, when bitcoin become a most stable currency then people will make bitcoin as a standard and then bitcoin will itself a standard for other currencies.
There is a possibility because bitcoin is not controlled by the government, its decentralization features likely to attract more people plus they can easily track their disbursements and receipts looking at the public ledger. It US will go cashless this will gives us good option.
It will not replace soon and that is because they can see that there are a lot of people that is getting to love Bitcoin because they want to make some profit of course and that is perfect.
But you never know what will happen with Bitcoin but it will replace maybe in the future.