Never going to happen. Governments are run by controlling things. If you want to replace dollar with bitcoin, you need to hand over the control of BTC to government. How a country's economy can be based be on such volatile thing.
If you see it from other angle, BTC can replace if every online business starts accepting BTC for transactions. They will still need to convert it to dollar.
You have a point. Before thinking on replacing dollar by bitcoin, bitcoin should be legalized first.
And yes it means that the government will have the power to manipulate bitcoins transactions and production. And we do not want this to happen because when government have the power to manipulate bitcoin, corruption may exist
Bitcoin is already almost fully legalized in a few countries (see Switzerland or Japan) up to a point where you can pay for public services with bitcoins directly. And did that give these countries any advantage in regulating or manipulating Bitcoin transactions or "production" apart from what any other country out there already has in this respect (let's call that "administrative resource")? How exactly does Bitcoin legalization give power or control over Bitcoin to countries going that way?