Worry less about selling out and more about selling
I once read a manuscript, a crime story about a cop who had a passion for Hummel figurines. This was a side interest in an otherwise tough guy, and the novel was beautifully written: lush prose, vivid characters, a genuinely tense storyline that revolved around a well-researched political scandal.
But still, Hummel.
The author had written himself into a niche without meaning to. The sum total of Hummel aficionados in the world doesn't outweigh the complete disinterest of the rest of us. And so despite having a great story with plenty of suspense, what the author had seen as a quirky character trait ended up labeling, and dooming, the book.
Writing a book is art. Art is personal. Your characters and story say something about who you are and what you treasure.
Selling a book is commerce. The rules of commerce dictate that the more people interested in what you're writing, the likelier it will sell, and the higher the price will be.
The trick is to find a balance that lets your art function as successful commerce. This isn't about hitting the least common denominator; it's about avoiding niches. They may be comfortable, but they're cramped, and you want room for as many people as possible.
It's a musical fantasy thriller, with lasers
There's so much talk about having a "big idea" or a "high concept" that aspiring authors often feel like it's not enough to simply write a compelling book. Admirably enough, they want to do something unique, something that breaks fresh ground. Unfortunately, many attempt to do this by mixing genres.
This is, by and large, a bad idea.
It can be done. It can even be done brilliantly, as in Joss Whedon's Firefly, a sci-fi television series about intergalactic smugglers operating on border worlds similar to the American Old West. It was an unexpected concept that worked. An audience will always respond to a forcefully imagined world. The problem is that no one knows how to position the finished product.
Think of it this way: booksellers need to know where to shelve you. If yours is a crime novel, they put you with Dennis Lehane and Lee Child; if it's literary fiction, they put it beside Michael Chabon and David Mitchell. If your book features blaster-wielding damsels tap dancing against the clock to prevent a terrorist attack, they put it down.
Genre is a marketing tool. It tells publishers how to promote something, booksellers where to stock it, and fans where to find it. So as temptingly fresh as cross-genre novels can be, they're risky. Firefly is the perfect example: the writing was spectacular, the world vivid, the idea original. Critics raved and fans swooned.
The network canceled it halfway through the first season.
In the midst of generic advice, there's this, which essentially ends up saying, 'Don't be unique, don't be creative, just be bland, and you'll do okay.' Which is perhaps is fine, after all: Sakey has published five books, been a notable New York Times person, has his films optioned, and even has Lee Child writing about his work. Me, I'm vaguely published, having gone through a number of agents, been told repeatedly I'm uncommercial, and don't even know Lee Child. My career looks about as good as it sounds. Still, I don't write articles that claim that Firefly is an unexpected concept that worked or that they didn't know how to position it. Possibly because I saw Galaxy Rangers as a child.
The poor use of my childhood is just one of the things that makes me a better author than Sakey. The other is that I don't tell people to not listen to their creative urges and condone the lack of creative in fiction by claiming that the use of Hummel figurines makes a book niche and only appeal to those who collection such things. After all, saying such a thing may lead you to believe that only murderers buy crime novels, that only astronauts buy science fiction, and racist shut ins buy Lovecraft.
You should ignore advice by authors like this. If you want to go out and write a fantasy thriller that is also a musical, go ahead. Do it. The truth about being published is that it isn't hard, and that there are thousands of publishers, big and small out there. You may not have lots of readers, but then, you may have many. A lot of people read a Mormon's sparkling vampire propaganda novel. Weird shit happens. But, if you write your book to make money, and only money, you are probably better using the time to go and become a banker; and if you want to write a bland novel that goes through genre tropes without no zeal, then go get a shit kicker job in McDonalds where you can mop the floor, flip burgers and give change to children. That's clearly where people with no thought process belong.
If you want to be an artist, try being an artist who knows their shit and is passionate about it. If for nothing else, it will stop people like me mocking you with cartoons for the eighties.