Thank you for the link!
Regarding every country having the same currency. Well, that would probably by optimal for the free market, would it not? And it would also be the likely outcome if you were free to use any currency you wanted in your region? The only reason to have your own state currency is to be able to centrally control it. That's why you are legally forced to pay taxes in your local currency and also forced to accept it as payment for debts.
I'm hard pressed to find an argument why any individual citizen would benefit from having a specialazied currency that is only bound to a certain geographical region.
This is a classic case of the resiliency benefits of diversity versus the efficiency gains of standardization. When one adopts a single paradigm, you can optimize around it and usually have a lot more speed in building things on top of the standard; however, mistakes, edge cases, black swains and other such things cause cascading failure. I would highly recommend reading this essay:
https://idcubed.org/chapter-7-complementary-currencies-necessary-financial-stability-scientific-evidence/ I do enjoy systems theory and feel its heavily underused in economics.
I think for the sake of stability and robustness the focus should be on digitizing all notions of value as tokens and then making the flow between them easy. Then we can talk about having a universal wallet that has allocations of tokens representing various stores of value and you get to decide the composition. This effort would result in basically total monetary freedom and a free market of paradigms. The best system ought to experience the highest level of adoption and use. The point is that we can now choose where before it was impossible to even consider.
