At this time the people who say it is impossible, but I would say this is very possible. If the user is bitcoin continues to increase, then there is no reason to make the bitcoin main priority and replace the dollar.
No it is not possible yet because behind Dollar there are many super powers who control Dollar and they don't want bitcoin to replace Dollar because bitcoin is decentralized currency and if this is happens then they loose their power. And if this would happen then bitcoin will be under control of someone.
soon or later but bitcoin has to replace USD. although in present time USD is one of the most strongest currency of the world but i think the users of bitcoin are now increasing from time to time, therefore we can expect that the price of bitcoin will replace USD.
NO I dont think so since the number of Bitcoin is never enough to adapt the demand of all people around the world. But it is a chance for other cryptos to appear and replace both Bitcoin and dollar