Worth reminding ourselves, with regard to the Brexit backstop, that nobody in fact knows how it will work in detail - because it is potentially so complex that negotiators have agreed to work it out by 2020 
Having followed Brexit commentary quite closely I don't think a single person has been through the list of regulations to be followed by Northern Ireland, and worked out what this will mean for north-south or east-west trade. I certainly haven't (examples below)
The backstop negotiation will undoubtedly be in competition with the future relationship negotiation, not to mention in the UK negotiations with other countries. Technically it will be challenging, and some issues could become political
This is one reason why I think having a backstop rather than extendable transition period is a mistake - it is a massively challenging undertaking for what may only be a short period, and it can probably never been entirely be satisfactorily resolved
