If the British Establishment were to bury the hatchet with the Republic Of Ireland, state visits etc etc. Then if the Irish republic were to leave the EU and join the British single market instead, suddenly there would be no need for a backstop as the Border with the EU would now be on the European mainland. Sure they would need to adopt the pound instead of the Euro and BOE interest rates instead of European ones. They could have their own notes with Irish Landmarks, historical figures like they do in Scotland. At the end of the day Ireland speak English not French, German, Spanish etc and are culturally aligned with the UK.