Thank you for parsing Shinto like this. Because of its "purity" proto-Shinto, seems the most interesting. Re musuhi, you mentioned Bergson and the elan vital. Musuhi also reminded me of the physis of ancient Greece, perhaps suggesting physis as a form animism, even if it wasn't perceived that way. Musuhi also might connect with Heraclitus' constant change, although musuhi is a more structured view. Despite their differences, it's reassuring in some way that very early thinking saw nature as such a universal force.