yes, Bitcoin will replace the dollar soon because dollar is not a world money. Though world accept dollar, is not a world money. Many countries use their own money. Dollar is also a money for some countries. But Bitcoin is not a money for any particular country. So, it can be used as a world money.
No I don't think so that will ever happen because the reason is pretty
obvious did you ever use gold to make payments no even though it is used a bit in world economy[1] , so
if we don't use gold as a method of payment then why would we use bitcoin[2] as bitcoin was made to replace gold so
why don't we just let it be a investment platform only[3].
[1]
Q: "Why do you think bitcoin will not replace USD?"
A: ".. because gold didn't."
Gold might be one of the major opponents of bitcoin but they are definitely not the same. Gold has a physical form but gold can also be in digital form. We haven't used gold as a payment method because only rich people do. The government uses gold to do large transactions to other businesses.
And by the way, with history we know that Gold was actually our fiat back then (i.e. Gold coin)
[2] Gold and bitcoin are two different things. Just because the other one didn't make it, doesn't mean the other one will not make it too.
[3] No one's trying to take away the capacity of yours to invest by holding bitcoins. We should not dismiss the fact that bitcoin is actually a currency, although it's being treated as an investment by almost all of us.