Im going to have to go with a conservative estimate of 5% of the worlds population will own bitcoin by 2020. 5% of the entire world population is enough people to create a country that has more people than the USA. There will definitely be more widespread usage of bitcoin as a payment method, and more governments will have to approve of bitcoin.
I think 5% for the estimated of the user of bitcoin for 2020 is very low because i think it is more than 10% now and it will keep growing because bitcoin is unstoppable and its price is keep on rising. The 3 years left will be enough for bitcoin to climb at least 20% of our population because we can see a lot of information that are keep spreading thru the internet and that will be a big help for bitcoin.
I don see where you could get the number than 10% of the human population is using bitcoin, in fact we dont even know the amount of people on the planet, the number is difficult to measure since some regions of the world like Africa dont have detailed records.