The main players are US, China, EU, Russia, India. Any new economy that involves them will force adoption by everyone else.

Disruption of the current system seems to be required, or it will be clung to. It looks like it has to happen in all major players simulataneously perhaps. In order of severity, candidates are: massive continuous cyber disruption, massive counterfeiting, EMPs, war, worldwide natural catastrophe, nuclear war. There may also be a nation level default cascade where all major players invalidate their currencies voluntarily, and there is a period of almost no trade.

In 2008, the US was able to engineer a set of circumstances which created massive instability in other world currencies by exporting vulnerability to them in mortgage packages. Amid all the chaos, the dollar emerged as the most stable. Removing such a massive amount of value from the system brought deflation to the dollar. The typically inflationary effects of 'printing money' were completely balanced by the deflationary effects, and the usual inflation of the currency relative to the other currencies was balanced by weakening each of them. It was rather an impressive masterpiece of economic warfare.

I'll continue playing later..