> They would be free to rejoin. Euro, schengen, and metricification are mandatory now though.

Well, in principle they could get unanimous consent on concessions again, they just don't come pre-baked.

There has been a lot of fuss about those concessions in the past, I really wonder to what extent the poorer EU countries that had no say in this when those concessions were given would be willing to give the UK something they themselves had to give up to join. That might not go over well and there are a lot of those countries now. That's a dangerous game of roulette.

It's not only a case of "we didn't get these deals". The UK got them, it wasn't good enough so they left. If they want to rejoin they are admitting they made a huge mistake and can they pretty please come back?

Imagine you have a job, with a few perks other employees don't have, and you want more perks. And you don't get it, so you quit, complaining about how crap your employer is. A while later you ask for your old job back. What are the odds of you getting exactly the old perks back? ;)

It is unclear whether it can be revoked, yes. It is also unclear whether it cannot be revoked. It's simply unclear.

Exactly. Once that court case winds its way to the CJEU we will have a clear answer on that question.