They are on the lookout for ...wait on it.....NARRATIVE NONFICTION.
Here is the advertisement.
"Got Narrative Nonfiction?
I'm often asked if there's anything in particular I'm looking for—usually the answer is just "good stories." But I am looking for more narrative nonfiction, telling true stories like fiction—this approach has great appeal for younger readers, and I'd like to get more of it in Ask. It could be the unfolding of a moment in science history, or a Flatland-type math adventure, or a classmate of Newton telling what it was like to go to school with him, or an apprentice blacksmith taking us on a tour around a Viking blacksmith shop. So if you've got an idea for a neat narrative nonfiction piece, or want to give it a try, pitch it! I'd love to see new approaches to old (or new) subjects."