you can't say at this point what will happen in the future. but as far as speculation goes i think it can be used by many people but bitcoin will not replace fiat.
True, and fiat will remain and be use over again since it came first and it contributes already in different countty, but the thing is maybe bitcoin will still functional up to 2022 but speculation and different possibilities may happened in near future . In behalf of this opinion I can say that bitcoin will be used by most of the people in near future base on its Potentials and huge amount of profit that a person may obtain .