So FNAF has books. Quite a few, in truth. Most of them are pretty bad, but the idea itself has potential. For example, the idea of an expanded universe anthology series set in the FNAF universe sounds really cool, but the goosebumps-esque way they went about it with Frights left something to be desired. Not to mention all the debates over the canonicity of the things. Honestly, I don't really care whether or not Tales is canon; the mimic storylines are cool and there's nothing too egregious in there (as far as I can tell). My issue comes with Frights. Most of the stories in Frights really are just bargain bin goosebumps stories with fnaf tacked on. Like, I know this has already been done to death, but faz-goo just sucks on an unbelievable level. Whether or not FNAF has a good story is debatable; one thing that's certain is that it's unique. Frights does not feel unique; it's lacking a certain element that the original story had and it just comes across as lazy and half-baked.
Truth be told, I wouldn't mind reading a book to understand the story of the games, given the book is actually good. Like, give me a Mike novel and I would eat that up in approximately one single afternoon. Unfortunately, the only fnaf book I actually liked was the Silver Eyes (and the survival logbook I guess). The other two books in the novel trilogy were ok, Frights and Tales kind of suck, and while the upcoming choose-your-own-adventure books seem cute, I doubt they'll have any real substance to them. Also, there's like coloring books and whatevers but who cares about those.
Speaking of very clearly child-oriented FNAF books, there's an upcoming sticker book apparently. The stickerpedia. Honestly, it sounds kind of fun, and I might actually buy it when it comes out. I'm not really a sticker guy, but I could be, especially if there's like Ennard or Mike or Mimic stickers in there. That would actually be kind of cool. My main hope is that they have stuff from across the whole franchise, because I could really see them having a bunch of FNAF 1 and SB stuff and neglecting guys like Molten Freddy. I suppose we will just have to wait and see. Perhaps I am getting my hopes too high; after all, this is the same franchise that brought us a character encyclopedia that was missing a page for the main character (never getting over that).
Also, while we're on the topic of the encyclopedia, I had a cool idea for how to make that an in-universe book, like the logbook. What if the encyclopedia was made by Mike, chronicling all the animatronics he's encountered over the series. He would probably be writing it in the interim between SL and FNAF 3, probably just as a way to pass the time and distract himself, maybe updating it later after seeing Fazbear's Frights and the Pizzeria Simulator location. Obviously, this would mean a lot of animatronics wouldn't be included, since Mike couldn't know about them, and a lot of information about them would have to be excluded, so it wouldn't be like a replacement for the out-of-universe one. That being said, I think having Mike draw the animatronics in his red pen (he is a good artist, after all) and write little notes for each would be really cute and a fun bit of fleshing out his character. There could even be a little story told through the book. Like, imagine Mike starting a page on Golden Freddy then scribbling it out and hiding his last name and stuff and then the last few pages of the book are on Fredbear and the bite and him revealing he's Afton's son and stuff like that would be kind of sick. Anyways, just some thoughts.