It happened last season for the first time when they showed The Night's King (and fucking HBO then blogged "The Night's King") which is something that hasn't happened in the books.

There are several characters who are out of book plot - Sansa and Littlefinger, Bran (for the most part). Unless they spend most of the season in Dorne, the Iron Islands and Essos - then they will have to eclipse the books for those characters.

Which leads me to believe that WOW will come out sometime early next spring so that the book readers are completely peeved at the show spoiling the books.