I just don't see it, cash is too easy for regular people, and such drastic change is difficult.
About developing countries I say clearly that there is no difficulty or the cloud of difficulty is very small because they have proper system for the Bitcoin and its users so they are comfortable with it.
On the other hand those who are using from countries where there is no proper system for the Bitcoin are with difficulties so they are not comfortable with it. Furthermore only for the Bitcoin and person with its knowledge will feel comfortable.