With any PoD predating it's extinction, how could the Pictish people and culture survive to modern times - or, if infeasible, to the early Modern period - as a distinct group from the Brythons, Gaels, and non-Celts of Britain? In addition, what impacts may this cause with regard to overarching British historical development?
At present, the best starting scenario I am aware of for this would be for the Pictish king Causantín to defeat and/or destroy the Viking invasion force that was battled at Dollar in 875. The defeat of the Pictish army is recorded as having been followed by a "great slaughter of the Picts" in the Annals of Ulster, a factor which may feasibly have played a factor in the steady Gaelicization of the Kingdom of Alba; at the same time, this may have been merely staving off the inevitable, given the length of the age of Norse raids in Britain and the low comparative population of Pictland compared to neighboring Ireland.
At present, the best starting scenario I am aware of for this would be for the Pictish king Causantín to defeat and/or destroy the Viking invasion force that was battled at Dollar in 875. The defeat of the Pictish army is recorded as having been followed by a "great slaughter of the Picts" in the Annals of Ulster, a factor which may feasibly have played a factor in the steady Gaelicization of the Kingdom of Alba; at the same time, this may have been merely staving off the inevitable, given the length of the age of Norse raids in Britain and the low comparative population of Pictland compared to neighboring Ireland.