Bitcoin has many advantages over FIAT, but it is very difficult to control the identity of the owner because of the anonymous feature. With this feature, I believe it is difficult for Bitcoin to accept as FIAT, but if it is accepted and approved. I believe that it will defeat and change the trend of all banks.
It's not anonymous anymore when they control, they don't need to control everyone's wallet as that is not impossible but they can always monitor the exchanges and businesses at any nature that would accept BTC because they can regulate it. I even think it would be easier for them to monitor due to the blockchain where there's always a trail they can find every time they will conduct an investigation, and this will also increase their tax collection since the blockchain is online 24 hours, faster, and cheaper, therefore more transactions means more taxes generated.