The real suggestion here is a renewable way to obtain crafting recipes. I could just suggest that any bookshelf that is of an already obtained crafting recipe and thus defaults to Nothing be randomly changed to an as of yet unobtained recipe, but that makes obtaining crafting recipes much easier. So I didn't want to suggest that. For that reason, I am suggesting this: Some sort of bookworm or other monster related to books that when killed has a relatively small chance of dropping a "Crafting Book" or whatever name works. Said book is destroyed/consumed when picked up and works just like a random bookshelf. This provides renewable bookshelves in a way that doesn't increase how easy recipes are to accumulate while still providing players a way to keep trying and hope that the RNG decides to finally be nice and give them the Magnetronic Plate Armor formula, for example. I'm obviously biased here, but I think this is not at all overpowered, I think it serves a use, and I don't think it clashes with the core game design. Of course, if the Wizard Lands can generate bookshelves and are re-generated every visit (I've heard the latter), then that renders this suggestion pointless unless added to the core game for those without the DLC.
There *Is* a Diggle Librarian. It is in one of the big four mods. FAXPAX, CES, ID or RR. Or it may have been TVoM... I just do not recall who made what anymore. These mods are great. Use them. You will be happy you did! Note that the Diggle Librarian in the mod does not drop books. It is just what it sounds like. They only spawn in a specific Library associated with the mod. But there are nine bookshelves if my memory serves me correctly. You will find them commonly on level one.
