I wanted to preface that I really like your work and your creative ideas for dialogue, interactions and scenes. I especially love everything concerned the book. Every scene and dialogue with it is great. 

I understand that you are working on multiple projects and time and money are tight, I just wanted to pitch 2 suggestions that I think would be great for the book plotline. 

First, I think more interactions, dialogue and scenes involving the book would be great. Maybe make the player show the book to for example Kate by smuggling it in their bag or projecting it on a wall something. I am sure you are more creative than me. 

Second, the way the girls get turned by the book is different then when you do it yourself. They are completely blissful, masturbating at any chance because they are constantly horny and are utterly devoted to the player (the books owner). As Julia suggests, it rewrites their thoughts and feelings, but their personality is still intact. I think it would be fitting if girls are enslaved this way get different dialogue and maybe even scenes in the bedroom from when they are enslaved by yourself normally. Just like the bimbofied girls from the Bimbo NG+ route who are different from the normal slaves. You could give the book to the girls in the bedroom to read to switch them to a "book slave" personality and then order them to switch back when you want. 

I think it would be a good addition, because for example Ashley (pre-cure) , Victoria and Reese are more or less unfriendly or hostile towards the player, but after giving them the book, their personality shifts and their dialogue reflects that very nicely. But the moment you talk to them in the bedroom, they are their normal selfes, even though the dialogue from before suggested they were so entranced with the beauty of the book that they physically couldn't stop reading and thinking about it and its owner. They should be ecstatic  and thankful that you showed them the book and its truths. 

These are just my two cents. Otherwise I am really excited for the next updates and what you have in store.