We're probably going to add it at some point, I was just trolling.
Hey, I'm a Norwegian with some historical knowledge who likes the idea of an Iceland tag, but is
outraged at the idea of an Icelandic culture in 1444 that's so often thrown around here. I know you didn't mention culture, but the idea is so abhorrently ahistorical to me that I'm gonna rant about it anyway. Let me explain why; I hope you'll read it.
At its earliest, Iceland was settled by Norwegians, and although the Althing ruled common matters in Iceland, it was still a Norwegian crown dominion, and continued to be so until the kingdom of Norway was dissolved. Norway and Iceland had fairly frequent communication and cultural exchange, and neither had all that much cultural exchange with anyone
else – most of Norway's cultural exchange was Norwegians leaving their homeland to settle Britain during the Viking age, although some brought Anglo women back home as slaves, which I suppose you could count as cultural influence. Either way, Norway didn't import much culture, and Norwegian and Icelandic cultures had not significantly diverged in 1444. They had started to, but not enough to call them different cultures, unless you also want to balkanise Norway into little three-province cultures (which would technically be more correct, but insanely pedantic, and also stupid from a design PoV) and split Sweden into Geatish and Swedish.
The defining point in history for the huge difference in language and culture that we see today was the Black Plague, which hit Norway
hard; Iceland, while it lost about as many people, wasn't politically affected at all, since it was so remote. Life went on in Iceland, while Norwegian society and political structure collapsed, and most of its literate class died. After this, serfdom and feudalism were implemented at much bigger scale in Norway, but the country was still absolutely devastated compared to its golden age a wee century before. As we all know, its political weakness culminated in the Kalmar Union.
Being Denmark's bitch and not a sovereign state for four hundred years did a lot to Norwegian culture, and to Norwegian-Icelandic interactions. Of course, Iceland and Norway had less interaction, because Denmark took over the role of overlord, and there was no longer a Norwegian state to communicate with. Meanwhile, the upper class of Norwegian society was largely informed by, or ethnically Danish; together with the loss of literate knowledge of Old West Norse, this caused the Norwegian language to slowly become... Danified?, to the point where it was barely recognisable as separate from Danish at all when Norway was given to Sweden in the Napoleonic wars.
Iceland, meanwhile, remained pretty much unchanged, because it was so remote. So, technically speaking, in EU4 terms, Iceland is still Norwegian to this day, while all of Norway was culture-converted to Danish and then had something like that shitty HAB event that culture-converts all of the Hungarian region to Hungarian, except modern Norwegian is still very Danish.
tldr: Icelandic culture in this time-period doesn't make sense, because Icelandic is 'real' Norwegian. You'd have to implement events about the decline of the Norwegian culture, and ones that made Norwegian provinces Danish automatically if owned by Denmark – but really, there's no point. It's a lot of work for two shitawful provinces, when the current solution is perfectly fine culture-wise. So we can just have a Norwegian-culture Iceland tag.