We must be realistic, dollar is the strongest currency of the world and dominated by USA superpower. of course they will do everything they can to keep it number one, bitcoin is hard to replace the dollar.
You are absolutely right. It will be very much difficult for Bitcoin to replace dollar. But there is nothing in this world which is not possible and there are likely chances that Bitcoin will replace Dollar in the future. We have already seen that Bitcoin is the top ranked Crypto Currency, so we can expect it to be the number 1 currency of the world as well.