There's been a lot of "oh my, the world is ending" about Amazon's foray into shared world fiction, which launched as Kindle Worlds in June.
In it, through licensed agreement with the original copyright holders, writers can set a story in another's world, such as Vampire Diaries, and receive payment for that story whenever someone downloads it.
After that, however, the ideas, the characters, the plot twists, belong to everyone who writes in that world -- not the original author.
The original author can still, however, continue with those ideas in the shared world and receive payment for any downloaded material that they actually write.
It is, as far as I can tell, the same type of copyright control already exercised by the publishers of Star Trek novels, Star Wars novels, or any "officially sanctioned" fiction set in various other shared worlds. It is certainly similar to the type of contracts writers receive for superhero fiction from the big houses like DC or Marvel.
This type of work always has been a hybrid beast, with writers earning either royalties or flat fees -- or a combination of both -- but relinquishing control over their creations. If you come up with the coolest villain ever to cross webs with Spiderman, you never owned that villain. Marvel did and always does.
However, if you wrote for Marvel, DC, LucasArts, etc., you did have long, long, and very detailed contract that guaranteed you payment. And, hopefully, an ongoing relationship with the copyright holder of those properties.
The caveat with Amazon Worlds, and it's one that giving fits to professional writers who depend on shared world income, is that you're not guaranteed payment. You can write about Vampire Diaries, but you won't be paid unless those stories sell. Also, you're not doing the back-and-forth with the holder of that copyright that most shared world authors do with the editors and publishers of these works in large houses. So you're not building a relationship with them. John Scalzi, the outgoing president of Science Fiction Writers of America, does his usual good breakdown on why this is a better deal for the copyright holder than the writer.
However you may be building a relationship with readers of this type of work that can translate into sales in other areas. Which is why some writers are giving this a serious look.
Am I interested in writing stories set in the world of Vampire Diaries? Not particularly.
But I'm interested enough to see how this develops to sign up for Amazon's newsletter about this project.