JD, you stated, "Wales is different. It is legally part of England and has been since 1536." it was but not since 1967.
The 1746 Wales and Berwick Act made it clear that references to England in Acts of Parliament included references to Wales and Berwick but that was repealed in relation to Wales by the 1967 Welsh Language Act.
Gladstone spent his declining years trying to guess the answer to the Irish question; unfortunately, whenever he was getting warm, the Irish secretly changed the question.
One should not encourage talk of a "united" Ireland. Attitudes won't have changed that much over the years. If a poll was taken and the decision was to remain in the UK then that could well trigger violence and terrorism by those demanding the dream of a United Ireland. If it was to leave the UK and be part of Eire then that could well trigger violence and terrorism by those insistent on remaining in the UK. We ought not encourage touching that one with a ten foot bargepole. The answer to this is totally in EU hands and their attitude to an airtight border. (Unless the southern Irish decide to leave the EU and join the UK once more.) If the UK can live with an open border and monitoring from afar then there is zero reason that the EU can't do the same, if they stopped making excuses.