My mother tells this story:
She was watching a friend's grandkids and they had gathered around their little table playing with Play Doh. My mother sat down and took up some clay and said, "Let's make bears!" She began to roll a ball. The boy next to her took a fistful of clay and mashed it into the mold and thrust it at her saying, "Bear!" He'd produced a bear-shaped mold of a teddy bear holding a balloon. The little girl took the mold and mashed the same bear and both children held them up proudly. My mother was not amused.
"Those are very nice," she said, "but I want to make my own bear."
She rolled out two large balls for the body and head, smaller balls for the ears, legs and arms, and tiny little balls for the eyes, nose, and little paws. She poked holes for the pupils and another for the belly button. The children sat, transfixed. They'd never seen anyone make a bear. It was unlike any bear in the box or on the cover or, really, anywhere else. It was if my mother had performed magic, which, indeed, she had. She then showed them how to make their own bears.
I know a lot of people get caught up in the question of "What's the next Big Thing?" or "What are the latest trends?" and while it's important to know your business and your audience, I'd like to point out that it's really not the right question: what you'd like to know is if your idea had enough strength to stand on its own in the market and that is due entirely up to the strength of your writing. A good book sells. People really don't want the "next Big Thing", what people really want--as my friend, "Fajitas" says--is the thing that makes everyone else want to be the next *your* thing. You don't want to be the trend, you want to be the trendsetter. You want to make your own bit of magic and redefine what it is to write the story you love to read. Write that book. Write what you love. As the always brilliant Maggie says, write what you always wanted to find on the shelf.
Don't aspire to fitting the mold, break the mold and make your own damned bear.
