With this consistent changes and upgrades to our life, i dont think fiat will have a role in this. Its obvious that modern society are highly automated and technological advancements are everywhere. I know there will come a time that even poor people have some devices to transact with. The government will know what to do.
looking at effectiveness, of course tomorrow people will turn to practical ways. but for evolution in that direction I think it still takes a long time, and dependence on fiat is certain. currently the best target is crypto payment facilities