Except Europe didn't simply switch to the Euro. Some members of the EU (plus a few others who aren't in the EU) switched to it, over a twelve year period, with

Except Europe didn't simply switch to the Euro. Some members of the EU (plus a few others who aren't in the EU) switched to it, over a twelve year period, with some others pegged to it (and maybe switching some day), some other countries adopting it 'unofficially' (i.e. it's their official currency, but they're not officially members of the Eurozone), and some countries who theoretically must join, voting against it in a local referendum, and thus deliberately failing to meet the entry conditions on an ongoing basis so as they can't join. (And this is, of course, ignoring all the logistical hassles involved in switching, never mind the much bigger questions, now very pertinent, as to whether trying to do all this may have been a cause of the downfall of Western Society, etc.) So I suspect this example gives more weight to the 'unlikely' side, than the 'yet...' side.