I agree with your thinking. The other question would be what is in the EUs interest.
Much as I like the Euro, it hasn't gone to plan. I suspect if the EU could back out of it gently, it would - but it can't. It even bailed out Greece to prevent the idea of a country leaving the Eurozone. Everyone who doesn't have the Euro now is either committed to getting it eventually, or has a very special exception, like the UK did.
The EU might not want to, therefore, write a side letter for a new applicant, letting them pick and mix on Euro membership, as it might make the single currency more optional and less unremovable.
That said, when there is a will, there is a way: the pound could be pegged to the Euro, exchange rate volatility dropped, and eventually you could have Euros and Pounds be like Pounds and Scottish Pounds (which are separate but fungible). If there is a will...