I guess 20-30% of people on Earth will own Bitcoins by 2020
This high guesses totally ignore the fact that there is not enough space in the blocks to make even one transaction for so many people in 4 years.
'We' use Bitcoin and think it's normal, 99.98% of the population does not use it.
I agree on 20-30% ,i also vote that percentage, my own opinion is because many people if they dont handle smartly or not earning much they will not continue bitcoining..also the factor that not all people knows how to use internet well.