Never. United States Currency is the worlds reserve note. All oil can only be bought with US currency. Other places like Zimbabwe currency is so far hyper inflated that they use The US dollar mostly.
US is a strong country with a strong economy, I guess almost all country accepts dollar and I can say it's dominant. Though in this world, fiat inflate it's value but not so fast with dollars. People has the choice whether to invest their money in bitcoin as we believe it will be big in the future but not to the point that it's going to replace it.
Well, honestly, I do not even understand what comes to the mind of the OP to think that Bitcoin will replace dollar soon. Seems so impossible as at anywhere you go, people are accepting dollars and they even look it greater than their own currency.
There is a very small chance that the bitcoin will repalce the bitcoin as the major reserve currency. That could be decades away.