Styles come and go. For the most part, old ideas are simply reinvented and brought out to a younger generation. Did you read my post on the Granny dress? That short-lived trend wasn't ground-breaking, just another case of making something old new again.
Literary styles change as well. Right now, Young Adult appears to be the crowd-pleasing favorite. But Fifty Shades of Grey was also a success. Do you remember when Chick-Lit was in? We also have Steam-Punk Gothic now. What is that? I consider it a hybrid--sort of historical/fanatasy/Gothic/horror. However, there are those more knowledgeable on that topic than I.
Still, it's confusing. There's nice list of sub-genres of various novel categories at Writer's Digest, but that doesn't include some of the "newer" classifications.
Will I write a Young Adult novel just because that is the current favorite? I don't know. In a sense, I've written a Young Adult novel--but it's set in another century. In Patriot's Heart, which will be released in February, the heroine is just eighteen, but she's living in 1778. That makes it a historical. Oh well.
My advice to aspiring writers is this: write what you want to write. Then fix it. But make sure you are happy with it. In the end, you are writing to please yourself. If you're lucky, other people will like it, too. It doesn't matter what genre or sub-genre it is. It's your story. Your style.
Start your own trend. Don't make something old new again.