No one can answer this correctly however i think atleast 1% or almost near to that of persons who uses internet banking will be using bitcoin by that 2022. But this number may even go higher if few good development as well as few more open minded politician come into power.
The current active user number is less than 1 million. So if the user number rises 50% a year, it will be around 8 million users then.
We cannot ensure that the figure is true because in the first place bitcoin is anonymous and any person can create different bitcoin address. So if you talking of 1 million, I think that is too big population for a number of bitcoin users.
There are 3 transactions per second at present, or 200,000 per day. If one active user use it once every 5 days , that is about 1.0 million users.