This came out in March, so it's more than a few months old and I'm not breaking any news here. I'm also sure there are other book trailers out there, but it is the first time I've seen something like this.
The movie/book relationship has been around forever - but usually one exists before the other and the trailer existed to promote the movie, not the book (there is no film version for this book). After seeing the trailer, it seems like an obvious way to boost readership for a series who's target demographic is likely to be motivated by visuals of zombies, ninjas and hot young women.
I've been intrigued by Pride & Prejudice & Zombies for quite a while now (solely on the book cover and title), but this trailer just convinced me to get the books (the trailer is for the prequel book - exploring how Elizabeth Bennett became such a great zombie hunter).The genius behind this series of books (as well as Sense & Sensibility & Sea Monsters, Android Karenina, and Abraham Lincoln, Vampire Hunter) is publisher Quick Classics.
It makes sense that a company that is reinventing old literary classics is reinventing the way that books are marketed.