Bitcoin has already become a global currency, It did this when it was trading on the Stock markets, yes as a stock, but also as a currency if you look at the stock exchange you have all currencies traded, and then the commodities market is also Bitcoin. so it is in all levels of trade, and currency exchanges, this is what keeps it strong, and will make it stronger for days to come.
According to me bitcoin current progress is very rapid(adoption), the more people who know what it bitcoin, how it works, and its superiority compared to paper currency, and certainly will be the currency bitcoin priority someday