I think what happens here is the rest of the UK exits the EU leaving Northern Ireland effectively still in the EU. Massive numbers of unassimilated immigrants and refugees relocate to Northern Ireland along with large numbers of young people who want to stay Euro cool and leftist professors, politicians, High Society Elites, and BBC personnel who all prefer cocktail parties and Marxism. Then. Insular UK. Grant’s Northern Ireland mandatory Independence.
God Save the Queen.
Then Scotland asks for the same No Deal UKexit.
Not really. NI would still be in the UK’s jurisdiction and under British laws.
immigrants and refugees would not be able to move to northern Ireland without getting papers and passing through the republic.
And they would then be subject to British laws, not EU or any other.
As to the other folks you mention - Belfast has few jobs, people aren’t going to relocate