During S4 Kit Harington, John Bradley and D&D had held a Q&A at the Oxford Union in which a spoiler was dropped that I had not noticed before. At around 22:00 of the video Kit makes a joke about 'putting himself in to a wolf' after responding to a fans question about how he would like to be a warg. 30 seconds later at 22:30 you can hear Dan Weiss say "Season 6, two more seasons". In Season 6 however we never saw Jon warg into Ghost. I believe that D&D changed Jon warging into Ghost after his death to Melisandre reviving him instead. I believe this is one of the future book plots GRRM discussed with D&D that they deviated from which also means that it would have been a 'last minute' decision to change as they would have been filming or already wrapped filming season 5s finale where Jon gets stabbed. I am also wondering why they would have even included this in the first place as Bran is the only warg out of the Stark children in the show.