I think that Bitcoin has not yet developed enough to consider the problem of overpopulation. It is still developing. It needs more people to support rather than start restricting the flow of people.
I agree, bitcoin is still in the process of developing. It's good to have a large number of people in bitcoin because it shows that bitcoin is trustworthy. But when a problem occur because of the bundle of people then it is the time to make an action to solve it.