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
Why do you think 16 and 17 year olds would be particularly interested in something that happened when they were 6 or 7 years old based on a vote that happened when they were 2 or 3 years old?
A sensible 2nd chamber idea could involve turning House of Commons into an English parliament, with HoL becoming an elected UK upper chamber for reviewing legislation from all 4 UK lower chambers within a federated UK.
Apart from the fact that the English electorate has no interest in a devolved legal parliament, your suggestion would:
– be much worse for Scotland and Wales (and nuclear for NI) because you’d have a UK legislature in a position to veto devolved legislation
– not have a space for legislating on issues that aren’t devolved to turn assemblies eg foreign policy.