I see 10% people worldwide using Bitcoin after 20 years. Just like Silver which was $80/ounce in 1980.
I'm sure that in 20 years there will either be very large transaction volume or no volume -- Satoshi Nakamoto
Bitcoin at $600 will also be valuable and will have long term future. Silver at $17/ounce is a precious metal.
The population, or the number of users is one of the factors that we can seen in order for bitcoin to be the future. It is predictable that more and more individuals will be persuaded to use bitcoin because of the perks you can have when you use it. Therefore the bitcoin is future, in other words with bitcoin we can have a good future.