I've wondered about this too. I live in the UK and have been idly daydreaming about my next startup, and it seems like Brexit, and therefore having a small market / uncooperative EU, is such a headwind for some of the things I'd like to do. Seems like many UK startups just pretend to be based in SF.
I think rejoin is going to be politically unpopular for a while, as there's no way we could rejoin the EU on anything like as good terms as we left on.
The UK is obviously too small and poor to go it alone forever. The other option for them would be economic integration with North America. They could probably join up with the United States-Mexico-Canada Agreement (USMCA) on relatively favorable terms.
That's far from obvious. The UK is 3x the population of Australia, which manages fine without deep economic integrations. The problem of Brexit is not that it is impossible to go it alone as a middle power; it's just an unnecessary handicap when you border a 450m head market but want to ignore them and act like you are an island at the arse end of the world.
Rejoin is polling far ahead of Brexit, which is beginning to be acknowledged as a mistake by everyone. Although not everyone agrees on the reasons.
The problem is the UK is an oligarchy owned and run by non-dom billionaires. It's essentially a floating labour camp. Virtually all the major industries are foreign-owned, and profits flow out of the country instead of being invested in infrastructure, R&D, and national development.
The public school/Oxbridge educational path is based on a 19th century view of the world, which has its roots in a feudal society that expanded into global piracy.
Rejoining the EU isn't just about undoing the direct, about exposing the population at all levels to a more modern culture with elements of social responsibility and rational state planning.
The EU isn't perfect. But Europe successfully rebuilt after WWII, while politically the UK is still stuck in the 1930s.
But that popularity (about 2:1 saying brexit was a mistake) isn't translating to political support, probably because both Labour and Tories supported Brexit.
And while the majority agree we should never have left the EU, and the majority agree we should rejoin, that isn't translating to political support.
Indeed the plurarity of votes is to Mr Brexit himself, who thanks to FPTP is likely to get a majority government in 2029 off 30% of the vote.
Hell 1 in 8 people that voted Farage last year think the UK never should have left Europe. Not that it wasn't the right type of brexit, but that it shouldn't. Yet they voted for Farage, decided that was a mistake, and are continuing to vote for Farage.
I get it. Some people just want the world to burn.
But a similar number think we should rejoin the EU, yet voted Farage last year.
It's no wonder support for democracy is at an all time low.
I think rejoin is going to be politically unpopular for a while, as there's no way we could rejoin the EU on anything like as good terms as we left on.