As has been noted, NI is a relatively phony political construct, gerrymandered into existence almost a century ago:

If all of Ulster (all nine counties) were to have a referendum, the Unionists would lose. They've always been in the minority province-wide.

If voting were on a county-by-county basis, only three or four of the six current NI counties would remain outside the Republic. Granted, they would be the most populous and most industrialized areas, but what legitimacy and what chance of survivial would an even smaller "statelet" have?

Irish Protestants probably had fairly legitimate fears about living in a united Ireland during most of the twentieth century, when the Catholic Church wielded inordinate influence over civil affairs in a theocratic young Republic. However, those days are clearly over.

It probably is just a matter of time before the most belligerant adversaries grow old and die off. As the younger generations grow up and take their places in the adult world, much of the ancient hatred (along with memories of the well-founded reasons for some of that ill will) will be forgotten.

I say, set a date! What was good for Hong Kong is certainly just as appropriate for Northern Ireland. And I agree that 25 years is probably too long to wait. If five years is too soon, certainly ten should be workable.