If an app like Kixie can use the existing native Call Activity type, I suspect that it wouldn't be too difficult to allow the LinkedIn Sales Navigator integration to access native activities if the options were added.
Love this idea. I want to know that my reps are requesting connections, adding connections and sending messages via linked in. I would also like to see the connection and the associated company to ensure these are RPCs (Right Person Contacts) or ICP (Ideal Customer Profile).