Frankly I think the ultimate outcome will be that Ulster leaves the UK and Ireland reunites as one island, one country.
Now that Ireland is no longer a Catholic country, offering free abortions for everyone, why would the North resist that?
The North has more restrictions on abortion than the republic has now. And you’re right - the RoI is far less Catholic.
Though I argue that the Irish troubles were less about religion and more about ethnicity - considering that the first President of Ireland was Protestant as were many of the leading lights of the movement. But they felt Irish (even if they were Anglo-Irish or Norman-Irish). Remember that Rees-Mogg is Catholic for instance, but seems the quintessential Englishman. The Ulster folks, about 30% feel British but they feel that “Britain” is leaving them, so might as well join the republic.
Oh and the Republic of Ireland and Northern Ireland jointly have a rugby team. the world is mixed up!