The poll posted above states 55% currently believe it was wrong for the UK to leave the EU. I can only see that increasing, especially if 16 & 17 year olds are allowed to vote in 2029 which will increase the electorate by 1.5 million.
Once the Tories are out of government I suspect rejoin will become an increasingly important topic and will be a 2029 election subject. The only party I see putting it on the table, who have a chance of government, are Labour now pro-brexit Corbyn has gone.
Right now though I suspect Labour see it as too risky despite current polling that 74% of people intending to vote labour stating they would also vote to rejoin. I cant see labour ignoring that past this election.