I expect (at least) one party will eventually adopt Rejoin as a distinguishing policy, and maybe sooner rather later.
But the appetite for Rejoin will probably depend on the shape of the UK economy and the political direction of the EU in 10+ years. If the Starmer project really has been delivering tangible growth by then, people may feel Brexit has (inadvertently) “worked” in the end. If the EU achieves greater and greater integration in the UK’s absence it may seem less palatable to enough voters.
Both of those are also going to be influenced by external factors like the direction of a possible Trump second term, the outcome of the war in Ukraine etc.
I would hypothesise now that the UK has left, France's proposals for a closer integrated EU standing army and two-speed EU are much more likely to go ahead.
Because of that I see a future in 20 years for something like a three-speed EU:
Full integration.
Free movement of goods and people.
Mutual recognition of qualifications and frictionless framework for EU standard goods back and forth across the boarder. With a seat but no voting rights for the discussion of said standards.
It'll take at least that long for the EU member states to forgive the UK for its fuckery. The memory of Brexit will have to fade enough in their minds before it's even considered.
It's doubtful that the same deal will be on the table, as it would be politically untenable domestically.
Getting France and Germany on board will be hard, given that they enjoy much more power in our absence.
The risk of our exit again when our xenophobia acts up would have to be objectively low, or no member state would take the chance on approval lest we fuck over their economy again when we throw an egocentric racist tantrum.
His optimism for Britain to rejoin the bloc is not matched by Jean-Claude Juncker, another former European Commission chief, who in July suggested it would take “a century or two”.
Somewhere between 15 years and two centuries is a good guess.
I hope so. Though 15 years may be a bit optimistic. The UK has passed through the phase of leaving the EU being a benefit in itself (freeing it up to rule the waves once again unfettered by the whims of politically-correct vino-drinking bureaucrats and such), and, faced with the sunk cost of its folly, has retreated into denial. Brexit may have cost us dearly, it goes, but it’s a price we have to pay to be true to our destiny, rather than pretending to be just another small country interchangeable with Spaniards and Belgians. Eventually the fit of pique will end and the consensus will settle on Brexit being a bit shite, and there not being any meaningful glorious destiny for which it is a price worth paying, and the question is how do we become like the Spaniards or Belgians (or, indeed, the Irish), enjoying the conveniences of the EU. It may take a generation though.
I can see the UK rejoining the EU in the future. It just makes sense for both sides. And 15-20 years might be a sensible time scale to get over Brexit, too. BUT: I'm not sure if the UK can afford to stay out of the EU for that long.
The problem is pride and British exceptionalism, like Polish people in the UK are "immigrants", while English people in France are "expats". Those expats form close-knitted communities, buy in their own shops, don't like to converse in the native language of the country, don't integrate well with the natives - exactly what the leavers said about e.g. the Polish people in the UK. Pride and exceptionalism made the "Project Leave" work. It was a "blue passport", "our fish", "souvereignity", "we can trade on our own", "they need us more than we need them" that powered the "independence" movement.
So the UK citizens need to overcome that and realize that one state fighting alone in a world of ever-growing Blocks is bound to fail. Any rational person knew this all along - but they were called out as "fear-mongers". And any rational analysis of Brexit must state that leaving was a monumental failure. But admitting that one has f-ed up on a big scale is probably one of the hardest things one can do. Especially as there are nearly as many people who voted "remain" and will tell the leavers "told you so".
I expect that the UK needs the time to realize how bad things can get outside the EU, and whatever makes the UK realize this must be harder than the hurt pride of admitting failure. And the UK will have to deal with some points that will hurt - not because the EU is out to hurt, but because things have changed since the UK joined the first time. And quite a lot of those things were actually started by the UK when they were still members.
I wish you guys all the best, and I want you back in the EU. And in the tiny little corner of the universe where I can help I'll surely do that.
I think we're waiting for a bunch of very stupid and very stubborn people to ... what do they say? ... "age out" of the voting pool.
There is a universe in which the Tories make rejoining a "sensible economic management" election pledge in ten years or so, in order to reinvent themselves as something electable in a post-boomer world. All we have to do is jump tracks out of the Stupidest Timeline. Everyone push the wall to your left, one two three NOW.