So in a governments aim to control our money it will leave a big opening for bitcoin and other decentralised crypto to exist along with fiat and will allow people to "trade" anonymously with each other over a completely independent infrastructure.
Individual transaction is hard to trace. But if trade on merchant, even using bitcoin, I am believe government can collect taxes and trace it. Government must be have good infrastructure to trace every digital transaction including bitcoin. What merchant need to accepting bitcoin as currency is government regulation