Thank you, that was certainly insightful. I see now that it is some kind of natural extension of relevant concepts.

I have been told however that from a formal point of view a lot of QM (maybe they were talking only about QED) makes no sense whatsoever and the only reason why the theory works is because many of the objects coming up have been redefined so as to make the theory work. I don't really know to what extent this is true, but if so I would still consider it a somewhat unnatural theory.