One idea I was tossing around was a stronger Danelaw (with the defeat of Wessex in the 860's) that encompassed the whole of England, as well as the Norse settlements in the Scottish Isles and Ireland. If Scandinavification was as extensive throughout Britain (minus the Scottish Highlands, Wales, and Connaught) as it was in OTL Norse-ruled areas, by the time that the Scandinavian kingdoms unite and Christianize, the High King of the Western Isles (probably based at York) will have a more than theoretical grasp over a largely Danish-speaking nobility that rules nearly all of Britain. The Norse who settled the North Atlantic and the Norwegians will likely be more sympathetic to him than the Danes and Swedes, and Denmark will be a constant opponent. Probably Britain will remain pagan and a refuge for pagans from Scandinavia until at least 1100. This kingdom would also be an excellent impetus for early prolonged European-North American contact, due to the fact it will likely be alienated from Europe and closely tied to Iceland.