If crypto usage continues to increase then I am sure that someday crypto will soon replace fiat, this is because crypto transactions are easier, cheaper and certainly safer than fiat transactions.
Is it really the case, though? When sending money, it's not really "easier" since both bank transfer and bitcoin transfer can be easily done with your fingertips. They both have mobile apps. I wouldn't say it's "cheaper" since bank transfer doesn't have fees as long as you are using the same bank, at least that's the case in my bank or in my country. Both are safe for transacting as well.
In real life, it's easy to take out a fiat out of your pocket and hand it to the seller and it is to take out your smartphone, open your data connection, scan a QR code, and send the money. They are both easy. For the fees, paying with fiat has zero fees and paying with bitcoin has, but it's so insubstantial that it's almost zero dollars.
The safety is where they aren't a tie. Let's say when you were taking out your fiat from your wallet, your wallet got stolen. It's okay since you can always just bring enough money to survive the day. You can bring as little as possible and wallets cost about 2$. But let's say while paying with your smartphone, your phone got stolen. Even when the bitcoins there is very little, the phone itself is very expensive and is pretty much what the snatcher is after.
But if you're saying "safety" as in "security" when sending the money.. Who got harmed by simply handing over a fiat? And who got hacked by simply scanning a QR code and sending money? Both are secured.