I know I've brought up this in this thread before, but how is the UK supposed to leave the EU, and also not have a border between NI and ROI, or some type of internal border between NI and the rest of the UK?
Kicking the can down the road is not a solution.
If they don't have a border, Brexit becomes nearly worthless, as an easy way to circumvent it would be to ship goods to Ireland, they move them to NI, at which point they could move to the rest of the UK. The same goes for people, granted they would be immigrating illegally and therefore couldn't legally work/reside in the UK.
If they can't figure that out, the most sensible thing to do is to cancel Brexit.
Honestly I think they should call for another referendum, due to this one issue. Its the elephant in the room that makes everything else really irrelevant.