What if the Wizarding world existed secretly in Will's world from His Dark Materials? And what if Salazar Slytherin knew how to cross between the worlds, and he was originally from Lyra's world?

This would mean that all of his descendants had external daemons--including Lord Voldemort. Given the nature of the connection between Voldemort and Nagini, could Nagini be Voldemort's daemon? (This discounts the revelation in Fantastic Beasts that Nagini was originally a human female with a blood curse--but I don't consider FB canon as it contains a great number of contradictions of the main Harry Potter timeline.)