Dude even in the future, fiat system will never go into extinction, that's traditional money we are taking about although I understand why you said in the future, may be you said that because we don't know what the future will be like but I believe that Bitcoin and fiat will continue to exist separately because both currency serves different purposea, people will continue to invest in Bitcoin, they'll take it for what it is but as for fiat itself, it has its own importance, let's also know that Bitcoin is not handy yet and we don't know if such will be possible in the future, Bitcoin is a store of wealth and value for the future, there many reasons why hodlers wouldn't want to transact with their Bitcoin on daily bases just as you said.
Exactly, that's why I said maybe since we don't know what the future would look like or if the evolution of money would change from fiat into digital currency with Bitcoin as the legal tender globally since it's more popular and better than other coins, but since we're not there yet we can't stop using the flat currency, I'll only advise people to invest their discretionary into Bitcoin but transact daily with fiat since Bitcoin would give more value to their money in years to come whereas ssving their money in banks would even attract debit for charges and so sort.