A bad precendent, much misunderstood
I really dislike Direct Rule for Northern Ireland because I do not believe they are like the Scots or the Welsh and doubt if they ever will be. The real British interest would I think be served best by pushing them towards a United Ireland rather than tying them closer to the United Kingdom.
The story of the right of the people of Northern Ireland to have a vote on Irish unity is a long and complex one. In its latest incarnation it is:
1 Status of Northern Ireland.
(1) It is hereby declared that Northern Ireland in its entirety remains part of the United Kingdom and shall not cease to be so without the consent of a majority of the people of Northern Ireland voting in a poll held for the purposes of this section in accordance with Schedule 1.
To understand how we ended up you need to go back to the Boer Wars.
In the century after Napoleon the British anglified the old Dutch colony at the Cape. The Dutch fled north establishing self-styled republics of which Transvaal and the Orange Free State acquired international recognition
These stood in the way of the British dream of a Cairo-to-Cape continental railway and the British attacked.
The mighty Empire was humiliated by the farmer’s republics but prevailed eventually and all the Dutch colonial republics were absorbed into South Africa. The cost of victory was surrendering the internal cultural war - South Africa was not be an Anglo-settler colony but a Dutch one, an Afrikaner one (and a continuing conspiracy of white against African).
The British goal during the independence struggle in Ireland was a South African peace - Ireland in Empire. But the internal political struggle in Ireland was one for ethnic control: protestant/British versus catholic/Irish majority - particularly in the north.
Ireland-within-Empire was to have 2 parliaments, and to reassure the northern Unionists their Stormont would need to give its consent for Irish Unity.
The retention of Ireland in the Empire was a dead duck, potent enough to cause the Irish Civil War, but Dublin just acted as if it were independent. The final underwhelming break came in 1949.
When the constitutional crisis in the North heated up and the first Direct Rule Bill was drafted in 1968, a good 8 months before the conventionally accepted first death of the modern troubles, this posed a legal problem.
The Draft Bill transferred the powers of the Parliament to the Governor General - if the Parliament could vote for union with the south, the Governor General could simply enact it with a stroke of his pen. And so the Unionist backstop was transferred from the Parliament to the People.
The Northern Ireland mechanism is a bad one for Scotland because it is designed not to enable and empower the electorate of Northern Ireland but to constrain the British Government. It is not practical nor invokable because that is not its function - its function is to reassure.