There will however eventually be a quasi-hard border on the Irish side. The UK - if it has any sense - will chop import duties to zero on anything we don't actually manufacture or grow in the UK. For example, we don't grow bananas, so why have an import tax on them? Similarly, we no longer manufacture tungsten power in the the UK, so why have an import duty on it?
Goods with zero import duties will be significantly cheaper than the equivalent imported into the EU with EU import tarrifs on it, so I expect there will be substantial smuggling from NI into the ROI, then re-export of goods from the ROI into the EU as 'EU' goods - no import tax on goods moving within the single market. The profits from that will be substantial and the bulk of the fraud will occur in the ROI - hence not a UK problem.
Had the EU not weaponised the Irish border question, I suspect a workable solution could have been found before now. As it is, I suspect the EU is in the process of creating a major headache for itself. Which is a classic case of shooting yourself in the foot.
Wordsmith