bitcoin is the top of crypto currency, dunno if it will be the king of all currency, you will not use bitcoin to buy 1 candy in a store for your kid. or a kid will not use bitcoin to buy 1 lolipop in a store, so basically USD or countries currency will not be gone because of bitcoin, some will use it some will not.
yes it is not possible at this time. but, maybe a few years things have changed. the development of technology. everyone could be planted with a number of chips in his body. so that the chips are connected to the bitcoin wallet owned. all Sycnhrone automatically.