For bitcoin, I don't think it's possible at all.
Governments do bot want to replace their fiat currency obviously, its better to ban bitcoin instead of let bitcoin dominate their official currency. Another problem, it's hard for bitcoin to reach scale implementation to afford so many transactions per second. Bitcoin supply is limited, can't meet the demand all over the world. Then, if bitcoin fail, all of those altcoins will fail as well.

no its not possible maybe for doggiecoin but not for bitcoin,

people need to do their business

no matter how hard i like this thing to happen.
i think it is not gonna be happening in the near future.
because we cant deny the fact that there are people who are not use in using new technologies or they don't have any intentions to do so.
and there are also others that do not have access to this technology.
so i guess there won't be a worldwide accepted cryptocurrency as long as there is this kind of people.

I don't think there will ever be a single currency that every country exclusively uses. There will likely always be other currencies that different countries use, though it is possible that each country does use Bitcoin to some extent.

If the currency is decentralized then that is completely possible

Bitcoin is a kind of currency where its value is decentralized wherever part of the world you are. This is the reason why many people predicted that in the future, bitcoin will be use worldwide as only one currency.  But, I doubt it will gonna happen.  It is very hard to change the culture of a certain place. Flat has been part of our culture in making any transaction.  Besides, it took many years to make all store technology ready to meet bitcoin standards.  Maybe in the future, bitcoin will be legalized and accepted worldwide and will be used as an alternative currency but not as only currency.

I think currency is a factor that can highy increase unity in the world. So, having only one currency can definitely adjust everything such as the trades and transactions of mankind all over the world to the point that each and everyone will understand and relate to whatever it is that each and everyone is trading, buying, selling, investing, etc.

I think this position is very difficult to become possible.Most people in the world do not make money through the bank.Most people do not have bank accounts.Most people in the world do not use a computer, smartphone, internet.The economy of each country is full of differences, and the tax and fees are different.People can only use their own country money in a normal bazaar.Bit coin is not a form of money. It is possible that bit coin only one currency in the whole world.

Impossible. Original bitcoin cannot function as a currency because of the issue with fees. It's only good for large transactions, and even then it still costs more than international wire fees.