Lets say crypto completely and utterly replaced fiat. Fiats don't exist anymore. All governments have seen the advantage of using digital currency and have completely changed their fiat into crypto, like dollar to dollar token(obviously not tether). How viable is this?
There are hundred of threads discussing this. You can search Economics section and get answer to it.
For example anyone can see how much I am holding using the public ledger and track me down and force me into sending them the cryptos I hold. I wanna discuss in reality if cryptos actually replace fiat how life will be and what are the problems we are gonna face and the immediate effects of it.
Even if everyone start using crypto, it is not possible that whole of your money could be tracked. You can send Bitcoin (let say) to someone and the other person can send you Bitcoins on your new wallet, whole money is revolved. This is what Bitcoin mixers do. It is impossible to track which address is owned by whom unless you using some centralized wallet service like Coinbase. As far as you create new address for receiving every payment and own private key of those addresses, no one can know how much you hold.