Sadly the FT is behind a paywall so almost none of us can read that. However if you don't have a "proper" border between NI and the RoI then you'll have to have one between the island of Ireland and Great Britain. Sounds good to me.
in theory, possible. But it has been ruled out -
1. It will mean immigration and customs checks for people travelling within their own country (the UK)
2. It will mean some citizens of the UK will have a fiscal advantage over others (ie being able to import reasonable quantities of cheap duty-paid booze and cigs)
3. It could hasten the unification of Ireland which...
4. Is unlikely to appeal to the DUP who currently hold this government to ransom
5. Should Ireland be reunified, what would happen to the British in Northern Ireland, especially those who wish to remain in the UK and leave the EU?
6. It also means the end of the CTA as our trade with Ireland would have to go through our own customs which would be effectively the Irish Sea ports (both sides)
But like I said, it's been ruled out by Davis and no Tory ever changes their mind. Ever....