First of all, as a modpack dev, this mod is incredible for me to use. The customization is brilliant.
My first suggestion is image support. In my pack I would like my achievement book to also work as a guide book. Images are a hallmark of good guide books.
My second suggestion is command support. What I mean by this is when a player completes a quest, a command could be run. For me, that would mean unlocking different crafting recipes.
These are the two things I want to see out of this mod. Everything else in it is absolutely stunning. Multiple guidebooks with custom IDs, recipes, and colors. Stunning.
Keep up the good work!

Hey, thanks fot the suggestions! I'm planning an overhaul in about 2 weeks so they come at the right time. First, I want to release a 1.12 version for the current code and then add some tweaks + features.

Images are difficult, but I definitely want to add them. They are much needed.

The command block support is a tricky one, but let me have a good think about them. Initially I want to add a "damage value" indicator, so you could see and probe the completeness of a book.
For individual achievements, I'm not sure yet. There should be a solution though!

Image support issue is #9 and the command block support is #18 :)