You know like Moby Dick..but in space
Dear Miss Snark,
In the role agents play as filters between editors at big publishers and the ocean of scribes "out there" how often do fiction editors request works on a certain topic or theme? That is, do you get editors saying over lunch or the phone “God, I'd really love to have a fresh timely novel on whaling and the Bible! Or, gee, where have all the Taylor Caldwells gone? I'd love to see another Tobacco Road Redux; a grit lit meth lab novel; grandma under the Tundra's wheels. You got any southern writers in your stable? (horse whinny in background).”
But seriously, do you mostly pitch novels coming from your writers? Are editors mainly passive and reactive to what you pitch? Or do they in a sense pitch ideas for fiction back to you? Perhaps it makes more sense for editors to stimulate books on nonfiction topics. "Need a book yesterday on nicknames and political scandals in American history! Gotta a writer who can scoot to the task?"
When I get requests from editors for certain kinds of books it is invariably non-fiction and pretty general: "I need more books for my marketing to small business" list.
I've never had an editor ask for Tobacco Road Redux but I've had lots of editors say "I'm looking for the next Lovely Bones".
Editors who love old books will frequently try to bring out new editions of the work. There's at least one story in the trades every year about an editor doing that.
So, again, and always, write your best stuff. Don't worry about what editors are looking for. Miss Snark will make them realize in short order that what they really NEED is your book.