>>18266044
It depends on how unified and centralized those states are/become early one because there’s still one major threat: the Vikings. Scotland probably doesn’t change much initially. The Vikings will conquer the Scottish Isles and Dal Riata and the Picts unify under the MacAlpins. But depending on the strength of the Brythonics, they can’t conquer Galloway and the Lothians. Scotland is thus much weaker and may never retake the areas controlled by the Norse-Gaels, as they did irl in 1266. Unless the Scots are lucky, you’d see a stalemate. When it comes to the Brythonic kingdom to the south, I’m inclined to say it does better than the various independent Anglo-Saxon kingdoms at fending off the Vikings. But who knows. If they adopt Charlemagne’s feudalism, then they may have a weak central government that still has problems with constant raids like the French. Maybe you get a second Normandy but in Yorkshire. Maybe they still lose and get conquered along the way, like a united England was in 1014. But, linguistic and cultural changes would not happen under Viking rule in the same way it did under Anglo-Saxon rule. If they survive it all in all, you probably get a Gaelic kingdom in the north stalemated with a Norse-Gael vassal of Norway. The Brythonics may remain a unified state and exert control over those conflicts by the 11th century. The question then becomes what happens through inheritance and dynastic marriages. It would be really hard to say what happens after that though. My gut tells me that Ireland is probably left alone since there aren’t a slew of Anglo-Norman adventurers wanting to conquer their own fiefdoms.

>>18266044
It eventually becomes Daneland because the celts are a weak and contentious people who would have easily fell to a Great Heathen Army.

>>18266044
The Gaelic Scots have would taken over instead.