"On Christmas Eve, an alien creature attaches itself to author J.K. Rowling. Suddenly, the real world is replaced by a magical reality influenced by the writer’s own imagination. The Doctor must battle witches and wizards to reach Rowling and put the world to rights.”
List of unmade Doctor Who serials (Wikipedia)
"I will come back to AMC’s The Walking Dead once all the children have been killed," is an impossible thing to say aloud but that doesn’t make it any less true.