As I understand, the levels are essentially supposed to be Yooka & Laylee jumping into various storybooks and retrieving lost pages. Well, that sounds fantastic! (Literally!) Now, I would suspect that all the levels that are supposed to be in this game are already planned out. But I would like to suggest the various was you could streeeeetch this concept even further in sequels!
What if Yooka & Laylee didn't just jump into storybooks? What if they could also hop into novels, cookbooks, instruction manuals, sheet music, magazines, catalogs, homemade books made by children from computer paper and crayons (stapled together), school textbooks, books with multiple stories inside them, newspapers, pamphlets, brochures, scrolls, superhero comic books, and even Japanese manga? The possibilities are endless! Anything that has pages! Get creative! Think about how the different genres can affect the level! Are there author notes? Letters to the editor? The description on the back? What about a "dedicated to X" page? What would you do with those blank pages at the beginning and end of books? There is a LOT you could do with the concept you've created.
And if you wanted to be really edgy, you could always have Yooka & Laylee jump into a satanic bible to go around killing demons, complete with a Doom/Tooie-styled FPS sequence, but I doubt that's ever going to happen.
I had always hoped I might one day see Conker revive the storybook present that appeared to be in Twelve Tales, and have him going around through dilapidated fairy tales, and it looks like I'll finally get to see some new heroes from the same team go ahead and take that to a whole new level!