Ok assuming what you say is even possible; to declare it a tax free event would cure the accounting nightmare (for average small to medium business) of offering goods and services in exchange for bitcoin. It would be an effective "blessing" by government, taking away the "only criminals use it" fud. It would pressure the federal reserve and us banks to offer ecash services and fluidity between your bank account and usd denominated ecash. They would demonize indefinite reverse swap usd denominated ecash token mints, because its direct competition with debt backed fiat notes. AML regulations would need to adapt to a world with no financial boundaries, otherwise they would force exchanges to only release bitcoin to covenant wallets forever bifrucating the blockchain between locked-to-whitelisted-wallet UXTOs and "legacy" bitcoin.

In summary, bitcoin would probably 4x immediately, but it is likely to result in a fork and the market will need to decide between government-controlled bitcoin and real bitcoin.