I just think of the brightest possible future, when crypto coexists with fiat.
Because in order for crypto to replace fiat, we need to have free IoT and internet networks covering the whole earth, everyone has the opportunity to access, own and use crypto payment tools, the simplest is a mobile phone with power and internet capabilities. From a practical point of view, when we still have so many poor people and living below the average around the world, we will not be able to see the prevalence of crypto in the near future.
In contrast, fiat, backed by governments, can exist and be used in the form of coins and banknotes that will be a more accessible solution for everyone in all circumstances.