Many countries do not have their own currency. Countries that use the euro don't have their own currency.
Duh? In the Euro case, the economic engineering is centrally planned and applied over all countries in the euro zone.
But individual countries have voluntarily replaced their currency with the euro -- something you said would never happen. Anyway, there are many countries that do not have a national currency. Adopting Bitcoin is not reasonable for any country right now, but it could be appropriate in the future for some countries.
Agree. There are a lot of countries which have substituted their currency with the dollar.
http://en.wikipedia.org/wiki/Currency_substitution
These countries could be ideal candidates.