Even all of us are using high technology I don't think cryptocurrency will replace fiat because they have instances that cannot cryptocurrency like when they have brownout and no internet. But fiat is all around even what happen you can use it and how the crypto depends on the price if don't have fiat.
I think that cryptocurrency can replace fiat money, we are moving in this direction. But for this you will need the approval of the governments and wait, may be, ten years.