Owners of the official MGSV Piggyback strategy guide can now download a pdf file which contains details of the final story mission (46). It’s lack of inclusion was to prevent spoilers. To open the files via their site you must enter a password, which can be found in the guide (first word on page 304).
They’ve also included the details regarding the the Nuclear Armament Event.
SOURCE: Piggyback
Metal Gear Solid V: The Phantom Pain – The Complete Official Guide missing mission 46 details