Don't think it's plausible, otherwise it would already have happened. I mean, if country X really wants to pull that card they could have already done so without having to tell the entire world of their invasion intentions.
We've had nuclear weapons for less than 100 years which is nothing in history. Based on that the Roman Empire never should have fallen. If it made it 100 years, why not 150000 instead of 400ish?
I think you are making a mistake trying to assess what "country X 'wants'".
It only takes one person to decide to launch a missile. And very few to execute on that decision.
And what an individual, or a country, wants can change.
Just because nobody had any desire to attack Ukraine with nuclear weapons at the outset, it does not mean that they will not decide to later.
Consider the fact that Putin likely thought he could get away with annexing Ukraine with little international backlash, just like the last half-dozen times he's invaded and annexed parts of other countries.
Now he is the sole leader of a country that is being completely cut off from the global economy, and made a pariah in the entire western world. The national currency, and nearly all international relations are nearly shattered.
The situation is very different than it was, and things are likely starting to look desperate.
I don't expect a large-scale use of nuclear weapons, but I would absolutely not write off the possibility of their use altogether.
