This is actually about seeing the banks and government creating one single currency to be used worldwide. Now, the question actually is that which bank will come up with this, and how are they going to be able to put up a framework or infrastructure to be able to let the whole world come to terms with the idea of using a single currency.
Apparently, this would just be a single centralized currency that would be controlled by maybe one world power by then, and in the case where the whole world is not under the same government, we have more independent countries these days that can as well just come up with their own currency on the blockchain, I see it hard to get something like this possible in the long run.
Speaking of banks and governments creating a single currency to be used worldwide, I believe that Ripple/XRP fits the bill quite nicely. It's centralized, regulatory-compliant, and a few banks have established partnerships with it. If successful, then banks worldwide could come up to an agreement (along with the Ripple company and governments worldwide) to launch a single currency living on the XPR blockchain which will be used by every nation on the world. As far as I can tell, it's possible to launch a digital asset or token on the XRP blockchain nowadays (read the documentation), making it a possibility for banks and governments to achieve said purpose.
Since everything is heading into the digital world, I believe that a One World Currency operating on blockchain tech is bound to happen within a few years from now. After all, blockchain enables transparency, trust, reliability, lower costs and higher security, which serves well the likes of banks and governments worldwide. They have realized this and have started to explore the tech more deeply. As such, it wouldn't be surprising when we see the world's major fiat currencies being transitioned into the blockchain within the future. Some countries have already launched their digital currencies operating on blockchain tech (like Venezuela's Petro currency) which means that there's huge interest from governments into acquiring and using this tech for their own benefit.
Now, all it's needed is for the Internet to gain widespread usage in every region of the world, and the creation of a One World Currency might become a reality. Just my thoughts