> It's just not true that syntactic borrowing is that uncommon (google it). That means that the historically documented prolonged contact between Scandinavians and the English had some effect on the grammar. No surprise there. Since syntactic borrowing is not uncommon in contact situations, it's a bad way to tell what language is descended from what other languages, so this proposal isn't off to a good start.

Agreed. An example is Japanese and Korean. They have virtually identical syntax, yet they are completely unrelated genetically. Outside of the vocabulary that they both borrowed from Middle Chinese, they have essentially no words in common.