Would it be possible to add a JSON key to allow pack makers like myself to create books that players can begin with in their inventory? Something along the lines of "starting_inventory": true.

This would be a boon to pack makers that want to use Patchouli to create a guide to the pack without requiring the player to know how to craft the book.

This is out of scope for the mod. There's other mods that allow you to give players a starting inventory.