There is just one problem with your analysis WP. It presupposes both sides being reasonable and using common sense. Only one side is interested in doing that.
The whole purpose of the withdrawal agreement from the EU side is to punish Britain. Martin Selmayr, the Secretary General of the European Commission has previously said that Northern Ireland is the price the UK would have to pay for leaving the EU, while the French newspaper Le Point quoted Michael Barnier as having said in 2016 “I’ll have done my job if, in the end, the deal is so tough on the British that they’d prefer to stay in the EU”.
The backstop is just a ruse to achieve the above aims. A hard border could easily be avoided by using the methods you describe in your post. Indeed that was exactly what was being planned by Ireland until Leo Varadkar became premier. The head of Ireland's own tax service said there was no need for any additional border structure.
So you may gather I'm not exactly optimistic about the chances of May's "re-negotiation" succeeding.
We can't say we weren't warned. Yanis Varoufakis predicted it all having experienced the EU's tactics first hand with Greece. He described their numerous tactics. My favourite one is the "Swedish national anthem". Basically it didn't matter what he said or how reasoned his case. The EU reacted to him as if he was singing the Swedish national anthem.