First off, there will be more risks and drawbacks to being a Devil Worshipper. As has been pointed out, they are a powerful type of Society and the rewards are great while the risks for members are rather low. Among other things, there will be more viciousness between members, a greater risk of discovery, and you'll run the risk of giving your neighbors a reason to declare Holy War on you.
The Hunt Apostates is also being juiced up. The Court Chaplain will now be able to find more than just extremely suspicious characters and the penalties for being branded have been increased. For example, you now also gain a revocation reason on the target. When an apostate is dragged into your throne room, you now get to choose one of three options; let them go free, imprison them or burn them at the stake (something that the AI favors). It's also possible, albeit rare, for your Court Chaplain to catch characters who are only a bit suspicious, secret members of another religion or - if the Court Chaplain isn't the most talented - innocent.
Next up, the Hermetics will be given a proper use for all those strange Ingredients they can pick up. You will be presented with opportunities to spend various resources in order to improve the outcomes (or negate the negative effects) of a multitude of - mainly - Hermetic events.
Another issue related to Societies is that the subversive religious cults are too invisible. The AI will now handle both creating and running the Secret Religious Cults more effectively. Right now, it can feel as if you are the lone actor in the society, but with the patch your fellow AI members will make an effort to contribute. Also, the general costs of certain actions (like evoking sympathy) have been drastically reduced in order to make running the Society more manageable. We also aim to make the secret religious cult system more dynamic.