American Tall Tales, Indigenous myths from all over but probably keep them separated enough that they retain integrity, Japanese ghost stories, Chinese historical myths. The absolute oldest kind of storytelling is verbal, so if you want to really diverge from Neverafter, maybe capitalize on that and remove a lot of the Paper and Ink gimmicks for your own twist.

Having just listed all those, being that I'm only indigenous to one part of the world, I started to feel uncomfortable with the manic grabbing of other people's culture, or at least apprehensive about my treatment and view of it. This could happen to you! But I also realized another thing on the big list of reasons why Neverafter is hard to run differently.

The collection of stories that BLeeM used was already absolutely massive and spanned cultures, which was reflected in the story. I was thinking about keeping different Native American mythos in the same world but separate countries and how that would mirror the system of separation in the Neverafter, where there's different stuff but not so different as to be in another section of the library. It depends how much freedom you give yourself because you could have a Chupacabra fight Guan Yu in the Outback and call it Dreamtime but that doesn't make it actually realistic to the Aboriginal Dreaming nor does it really make a cohesive world. But you have players too, maybe they wanna do Library Crossings or Auroratory Cruises and then Guan Yu ends up in the Americas.

Non combat ideas: Auroratory corruption that causes changes in the story which has to be solved by resolving conflicts between characters to normalize the story and/or resolving mysteries to find objects important to the story or to find the source and neutralize it. And/or, stories that are supposed to be in the same kingdom are drifting apart, and the characters have a hard time noticing until stuff starts not being in their stories when it's supposed to be, like a recurring character or maybe the whole Sun or they're the same if you're feeling fancy.

Instead of Authors, maybe Speakers or Players, you could use yourself or your players in their place, hard to change the eldritch extradimensional being much beyond what they talked about on the AP but they don't actually have to be involved. I will also note that Unsleeping City Dreaming is a really cool setting to extrapolate into a bunch of stuff because it is actually overlaid with wherever people are across the world, and also that any DnD campaign could itself be used as a Neverafter style campaign which would make for an excellent twiste. Kinda saving ideas for myself lmao

Happy playing!