I certainly agree that there should only be one currency in the world. This would address a lot of problems, unnecessary problems. Foreign exchange itself causes a lot of problems. During the gold standard, one could easily do business across nations without worrying about the fluctuations in exchange rates. Valuation of goods and services has a single standard. There's ease and convenience in doing business.
Indeed, introduction of a single global currency can really work lots of wonders in reformation of the currently existing global financial system as well as addressing a lot more economic problems that storms the international markets. This involves the removal of the need for foreign exchange. This would be the first step towards the reduction of transaction costs and also to simplify international trades and finance.
Although, while the gold standard you aforementioned may have had its own issues and limitations, it sure did play a very vital role in stabilizing the global trading system and also made it a lot more reliable for people to use.
Even when the gold standard was drastically abandoned due to a variety of problems such as restrictions on monetary policy and the complexity of maintaining the link between the gold and the traditional fiat system, we still can't discredit the fact that the gold standard had been tremendously helpful in the trading system.
However, in a selfish world where one country competes with another, tries to dominate or subjugate the other, struggles to be more powerful than other, greatly benefits from the weaknesses of the other, it's hard to be implemented. And then there's the sovereignty of every country. One country whose local fiat is a big failure would rather create another one than embrace a different country's fiat.
You're also right about National sovereignty and competition being one of the major obstacles and problems that is strongly fighting against the adoption of a global currency. A country's currency is mostly seen as their symbol of their identity and sovereignty and giving that up and adopting a global currency would mean for them, giving up their sovereignty and control over their monetary policy to a global entity, which is almost impossible for Manny countries to come to terms with.
And again, it's possible that one country's financial interest may completely differ from others, which makes it almost impossible to merge the both countries into accepting to make use of one currency.
Let's just take the US dollar for instance, we know that the US dollar has been enjoying the privilege of being the world's reserve currency, so it'll be typically impossible for them to agree to give that up for anything. Because that'll be giving up their major advantage over every other country's economy and financial systems.
Bitcoin somehow addresses this problem. If Bitcoin would one day become the native currency of the internet, which is more or less the global community itself, then there's at least that single denominator shared by everybody across the world. However, let's forget about it being a solution to poverty. It isn't.
You couldn't be more correct about this. Bitcoin's decentralized nature and it's global accessibility makes it a considerable option and a possible substitute for the traditional fiat system, because Bitcoin has contributed in solving most global economic problems so we can confidently say that Bitcoin has the potential to become a global currency.
Concerning poverty, you're right too, since the main poverty cannot be entirely blamed on the traditional fiat system, it'll be completely wrong to say that Bitcoin or a global currency would completely eradicate poverty. But Blockchain technology possesses the power to completely transform the the current financial system in a way that it could address the main issues that contributes to powerty such as the exclusion from making certain financial decisions that concerns you as an individual and also individual's inability to access certain banking services, amongst several other problems.