You may have read the news today about JK Rowling's new title, which will have a decidedly adult theme. The author hasn't said much more than that. No explanation about what exactly the subject matter will be beyond the fact it will be intended for an adult audience, and not for children.
Doubtless there will be many disappointed parents and children who have been longing for more adventures from the world of Hogwarts, but really, Rowling must be at least somewhat tired of writing about it. Besides, since her first Potter book was published in 1998, many of her fans have passed into adulthood. This means she has a built-in audience for new books, different books, "adult" books.
Regardless of how well her new books are received, Rowling remains the author of the fastest-selling book in the history of publishing. She invented an entirely new universe of characters; saw her books translated into more than 70 different languages and had them turned into one of the most successful film franchises in history. All of this success translated into real dollars for Rowling who has come a long way from the dire financial straights she was in when she first started working on the Potter series.
As a writer myself I certainly cannot claim to have found the same success as Rowling, but I can relate to the feelings of burnout I get from writing about the same subject over and over again. I write short stories, mostly, for just this very reason. The characters, settings, themes and subjects change with each story, which helps me, as a writer, feel better about the work I do.
I wish Rowling much success (although she hardly needs it) and more than that, I hope she can rekindle the joy of creating something fresh and new that speaks to her heart, instead of her bank account.