Of course the price will immediately rise, if it has been accepted by all countries, even at this time perhaps large companies are preparing to buy if regulations regarding BTC or news about BTC goes well.But it's just a matter of time.
Just to be real though, the price is not going to immediately rise even if bitcoin is going to be accepted universally. It will go on a process and as we know that we have bull run and bear market season.
So it's not just be a matter of time, on the contrary it might not happen soon. As we all know that there are countries that are still against crypto in general. Only El Salvador and few nations have accepted it as legal tender. So it's going to be a long battle in the next decade to see that bitcoin is universally accepted or not or USD will still be the preferred medium of exchange although several countries has started it's dollarization.
Governments prefer more stable currencies and they usually hate significantly fluctuating currencies so it will be very difficult for all countries to accept bitcoin as a currency.
So it's hard to imagine if all countries accept it, at this time it is still impossible even in the next few decades bitcoin will definitely be more against it, the government just wants control over them and can control everything, then bitcoin is difficult to control so more against it than accept it.
Still the local currency of each country will definitely be maintained even though it is drained by inflation but people still believe because there is a government that guarantees it.