Fantastic pack, I'm loving it and I'm disappointed I'm almost done all the quests!
I'm not sure if you take suggestions, but I'd very much like to see a Spawn Coven Witch quest, most likely unlocked right after the Hobgoblin quest of the same type. I can't be the only one who doesn't love roaming thousands of blocks just to (maybe) find a couple of these suckers, and even if the recipe were expensive it would be well worth the effort to be able to cast the Coven Rites more easily, not to mention it fits in perfectly with both "The Life of the World" and "How the World Changes".
I spent some time thinking on this suggestion, and a recipe I think would fit perfectly (both thematically and expense-wise) is:
3 Experience Drops (included in all of your Spawn Egg recipes)
Spawn Hobgoblin (common-sense progression from Villager -> Witchery-style Villager -> Witch)
Brew of Love (not too expensive, and gives it the flavor of fertility and life...)
Brew of Raising (not too expensive, and gives it the flavor of raising an entity from nothing...)
Seer Stone (a bit expensive, but gives it the final spark of magical intuition and knowledge...)
This way, you've made sure that to craft this, the player has already completed "Which Came First?", "Hrrm", and "Mentats Minions" in "The Life of the World". You've also required them to have a functioning Witch's Oven (Whiff of Magic in Brew of Love), Distillery (Oil of Vitriol in Brew of Raising), and Altar (Seer Stone) - the latter with at least 2000 power, which is respectable but basic.
I might be adding this to my world via whichever tweaking mod(s) you've used for the other recipes and I'll post back here with updated thoughts, but I'd love to hear everybody else's opinion on this as well.