So what does this mean for the aspiring author? If you're going to write to the trend, do so at the beginning of it. Look at the 50 shades phenomenon. D/S bondage erotica wasn't exactly mainstream. Publishers didn't have anything comparable to market so they could ride the wave. So they snapped up self-pubs and reissued anything similar, like Sylvia Day's older titles. Day's Bared to You, by the way, was originally a self-pub. You can get the story of its journey to traditional publishing straight from the source via a Dear Author podcast.
If the wave has hit, however, you're going to have a much harder time selling. For example, when The Hunger Games came out in 2008, it launched the YA dystopian trend. Readers were looking for something to tide them over in between books and publishers wanted to meet that need. Two years later, books in this subgenre began to roll-out: Matched by Allie Condie in 2010, Divergent by Veronica Roth in 2011, Delirium by Lauren Oliver in 2011, Enclave by Ann Aguirre in 2011, The Darkest Minds by Alexandra Bracken in 2012, Under the Never Sky by Veronica Rossi in 2012. Yes, dystopians existed before the odds were in our favor (The Giver by Lois Lowry in 1993, Uglies by Scott Westerfeld in 2005), but Katniss was the match that lit the flame. It's now 2013. Editors and agents have been flooded with dystopian YAs for FIVE YEARS. Your manuscript has to be pretty damn spectacular to stand out in the slush pile, let alone to get an editor to gamble the readers won't be burnt out on dystopians in 2015.
How do you predict the future? Personally speaking, I look for the match. If I can pinpoint what might spark a new trend, I can get ahead of it. I check out the TV pilots for the next year's season, glance at upcoming movies, and I read the trades for what's being published next year, Publisher's Weekly in particular. I'm active on social media, I talk to young adult librarians, and I look for things that I, as a consumer, might enjoy.
I've long been an advocate for more fairy-tale based books due to Once Upon a Time and Grimm. My boss has been actively searching for high fantasy and the fact that we have three Hobbit movies rolling out make this a safe choice. I think outer space/science-fiction might make a bit of a bounce-back and personally speaking, I'd love to see a YA where the future doesn't suck, like a futuristic contemporary.
But if you have a fantastic manuscript, one that makes your critique partners cry or sigh or gives them nightmares, it doesn't matter what genre your book is in. A wonderful book will always sell eventually. Who knows? Your book could be the next match.