I don't think there ever will be a government willing to fully adopt Bitcoin as they can't control everything around it.
Agree, I've never seen it as plausible scenario.
The only countries that could realistically declare Bitcoin as official currency are micronations like Sealand or Liberland.
Other scenario, less likely to happen, is when BTC grows to solid payment alternative in some 3rd world country, then if their main currency collapse, bitcoin could naturally replace it (although temporarily).
That doesn't say they won't make a Bitcoin clone for themself where they control every process in full. That's more likely to happen at some point in the future.
They'll likely move towards blockchain-like technology in the future, but whatever it will look like, it will surely be centralised, so I wouldn't call that 'bitcoin clone'.