For bitcoin to be treated as a legal currency it have to be a legal tender to pay the taxes with. That would mean that either:
1. Payment in the public sector would be partialy payed in bitcoin.
2. And or bitcoin departament should be made. Its job would be manage the bitcoins colected as taxes.
3. The central bank that issue the money for government must accept the bitcoin.
The third option in my opinion won't happen, and the 2 others are highly unlikely.
I basically agree with all three options you enumerated
And also with that they are unlikely to be implemented any time soon by any major government out there. That said, there is still a lot of room for movement on the government's part (let's call it Bitcoin tax maneuver, as they say in some countries). For example, they may not accept Bitcoin as a universal legal tender for payment of all taxes (public debts, etc), but they still could agree to accept Bitcoin for Bitcoin ("an eye for an eye" approach, so to speak). That is, they could take bitcoins as a payment for Bitcoin related taxes. Say, you increased your capital from 10 to 15 bitcoins within a year, i.e. you earned 5 BTC of pure profits annually, and the government might hope that you will want to pay them something like 10% of your profits (0.5 BTC in this case) as bitcoins, not as dollars or whatever