Nice articles, but in my opinions i can hardly think so, just like you mentioned it will be difficult as the existing worlds had a lot of means to manipulate foreign exchange as a form of political power control between nations. Those political issue will not likely resolve unless there is a greater common goods. Yet the use of single currency world wide likely only benefits individuals like us in a much microscopic view compare to national wide decisions. Lastly, different development state of different countries and different living standards will lead to different value of the currency in different part of the world and this would likely create arbitrary value of the currency! But of course as a microscopic individual i would like to see single currency being use world wide!!