2) Like how most Irish people still consider themselves Catholic...
The 2 largest opposition parties are both primarily marketed as Republican parties. Even if their policies aren't focused in that direction I hardly imagine either FF or SF will just drop the republican element of the party, because republicanism is unfashionable in some Munster/South Leinster county that has no fucking idea where Derry is on a map, or think Monaghan is Northern Ireland
Bear in mind many in Northern Ireland are 100% Irish citizens and therefore the exact same as anyone born in the Republic and entitled to the same rights so Northern Ireland whether United or not will ALWAYS remain a big part of the political agenda here. Even if FG can't identify on any level with Northern Irish citizens. (Although can they identify with anyone
Regarding Korea, they were unnaturally divided in the 50s just like Ireland was in the 20s so yes add 30 years and two massively different ideologies and yes its different to Ireland but thats about it.