For a given country's population, if the share of bitcoiners was the same in every country, Americans would only make 5% of all transactions. On the other hand, if using bitcoin is relative to the available wealth, the U.S. will keep on dominating bitcoin for many more years.
I think south euro countries may start becoming the main countries in term of transactions volume, also then later on add all those poor countries without banking system once with SMS technology you can do more than enough to operate with BTC.
I had a vacation last summer in Greece. I have met/drunk with many people, telling them about bitcoin (yes i do that evangelism a lot, if the situation is right:). One of them is opening a restaurant this summer, and i educate him about bitcoin accepting options, for he is invigorated.
There are literally ten to the hundreds of thousands of people all around the world who spread the bitcoin message EVERY DAY, in an ever exponentially growing numbers, all around, and many people listen. It follows the power law f(x), and can not be stopped or slowed down. The first time i have heard BTC was in late 2013, since than i have had the Nicosia online course on cryptos, read books, listened like 400 hours of videos, gone to conferences and "converted" 3 of my best entrepreneur friends; all started or going to accepting bitcoin in their business this year!
I am actually surprised how fast this is spreading among my societal circles, even with older generations (50+). We are definitely gonna be surprised how fast the tipping point is going to be reached; it is proving once more how the exponential can not be comprehended by humans