Both Northern and Southern Ireland totally refuse to have anything other than a fully soft ,open and unrestricted border. So yes, I can see no way that the rest of the UK can leave the customs union.
Scotland ,Wales and London have all said that if Northern Ireland is allowed any type of 'special relationship' with the EU , then that relationship MUST also apply to them as Northern Ireland is as much a part of the UK as they are.
The only way we can possibly leave the EU is to leave in name only , all else has to remain the same, including freedom of movement.
This is precisely what I said and predicted months ago.
We will be worse off as we still have to abide by EU decisions but will have zero input in making those decisions. Even worse we will have to pay £35 to £55 Billion for the privilege of gaining nothing but losing some of what we already have.