It's currently estimated about 3 million people own some amount of Bitcoin.
That's about 0.3% of the population of Europe and North America.
If Bitcoin becomes mainstream, and say 50% of people in Europe and NA own Bitcoin, how much would it be worth?
Amount of people that own it does not matter. Demand matters. If lets say 50% of the people
want to own Bitcoin but don't have it that would drive the price insane.