See such a thing right now seems to be very unrealistic and hypothetical if we think about it.
But what I think is such a thing can happen that banks are used less than bitcoins.
But for that bitcoin trading will have to be much more efficient than now.
What I mean to say is that transactions should confirm fast and also transaction fees should be reduced.
But I don't think such a thing would happen at least till 4-5 decades from now.