Outcroppings of Fiction

Interesting story in the Wall Street Journal about the fact that many unknown writers are achieving followings by writing stories that jump off pre-existing books. Case in point, there's a lady that is writing stories about Harry Potter's grandparents.
Hmm. I wonder if I should do something similar to jump-start my non-career as a novelist? Perhaps I should write a tale about Sidney Carton's grandmother? A Tale of Two Teacups. Or maybe a short story about the Grinch's uncle Feester? The Feester Who Keistered Easter.
Or maybe not.