Norn Irish boyo here. Just want to add that the demographic data on Northern Ireland is fascinating when it comes to the topic of reunification. The Wikipedia pages on both united Ireland and Northern Irish demographics are surprisingly detailed if anyone is interested.

It's true that votes for Sinn Fein have been steadily increasing for years, but it's also true the demographics of N.I have been slowly shifting in their favour for years as well. The amount of people that consider themselves Irish or catholic have increased, and those that consider themselves British or protestant have decreased. The writing has been on the wall for the unionist parties that this was coming for a long time.

It's also of note that big support for Sinn Fein and even republican parties doesn’t necessarily translate to big support for Irish reunification. I believe polls show it getting closer but they'd still almost certainly lose a border poll if they called it anytime soon. Unionist voters are obviously staunchly against it but I think many Republicans get cold feet when thinking of it happening right now and not "sometime in the future".