Oh, that's a fascinating possibility! So he could be "the pure-souled cunning man" who's ambitious to save the world (or at least his community). Iirc the Fenlands were part of the Danelaw, so he could definitely be "from fen" and have a Norse parent.

I also remember reading some speculations that Helga Hufflepuff was descended from the Vikings who settled in Wales (they had a few apparently). I guess part of this is based on the "valley broad" clue, but I'm not knowledgeable enough about the geography of the island to verify that. Anyway, if she's from a Norse family, and one of Sal's parents is as well, maybe there was a family connection there - friends, trading partners, maybe distant kin - and that's how they initially ended up meeting or corresponding about magical scholarship and, with a couple of friends, eventually decided that hey, we need to do something about magical education on this island. I have an alternate theory where the Founders were all originally attached to monasteries and other church organizations, since that's where you got an education in those days, and they found each other through those channels. But there's no reason a couple of them couldn't have met other ways.