Seeing that the currency Brexiters are dealing in is pure fantasy with a sprinkling of Unicorn tears, I've got a solution for you. One that will keep Scotland in the EU while respecting their indyref result. That will keep the Irish border open, the GFA intact yet ensure NI stays in the Union. At the same time, it will allow the hardcore English brexiters to enjoy the hardest, closed-bordered, most Brexity Brexit that they can fathom...
It's simple really.
Article 50 will be withdrawn immediately and England will, within a period agreed by parliament, leave the UK.
The new sovereign England, a state in its own right for the first time in centuries, will be free to close itself off to the rest of the world. They can, if they wish, build a literal wall (or steel spikes are in vogue, I hear) at the Scottish border. 'F*$# you, Merkel' will be daubed in massive letters across the cliffs of Dover. Border agents will have a handy colour card, like those wee Dulux ones, so they can ensure only the whitest whites are allowed in. Potential immigrants will be asked to recite lines from Only Fools and Horses and Dad's Army. Boris Johnson will be driven around the former colonies by Prince Philip (apart from Ireland, DON'T mention Ireland), dancing with natives and securing the most TREMENDOUS trade deals imaginable.
Wales can, if they like, choose to leave the UK as well. Maybe they'll want to go it alone, or maybe they'll join England to create a new union - call it UK2, or Br1ta1n for the nostalgists.