I think it will not replace fiat for quite long time. i could not imagine my grandfather handling crypto. so still there is a lot of work to do to ease the whole process for everyone! How do you want to make children pay for stuff? Will there be prepaid crypto cards? But in the future I think when the developers find solution for all these little things, then yes one day crypto could really replace fiat. i dont know if in 10, 20 or 50 years?