From its inception in 2009, Bitcoin spent its first five years in obscurity before coming to light. Seven years down the line, it is the most sought after digital currency. Even though Bitcoin is now a widely recognized cryptocurrency, it is still an alternate currency used by less than one percent of the world population.
http://www.newsbtc.com/2015/12/06/why-bitcoin-makes-an-ideal-reserve-currency/I would place at bitcoin user numbers somewhere less than 7 million ... that's less than 0.1% of the world's population. In the end however, for bitcoin to be considered not an alternate currency it will not be number of users but total wealth value bitcoin is utilised by, i.e. top 0.1% of population controls vast majority of wealth.
