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.
Yes, it is possible only in the case when bitcoin will begin to control and make of it paper money.