Since nobody else has expressed an opinion, I'm actually going to move ahead with the plans I mentioned. The next update will be out in the next couple days and won't include any of it, but will have some new reactions available to fortresses, especially the dwarven magicians civ, to give access to new and interesting things. First up is the ability to transform female llamas you own into a spider-llama, a sterile female that produces silk cloth instead of eggs, milk that can be processed into silk, silky fleece to shear, and sprays silk webs at attackers. There will also be the option to turn your dwarves into vampires or were beasts, and some other fun things at the holy altar.
I don't plan to make these all available to the vanilla dwarf civ, but they'll have some unique ones too.
The human magician civ will get some too, eventually. They'll be more organized around beneficial, benign effects compared to the dwarven sorcerers' power-hoarding, sometimes destructive effects. Neither is really supposed to be good or evil, but the cultural differences are meant to revolve around the proper use of magic in society related to their spheres and available schools.
We also get the spider queen megabeast, which has necromantic powers to summon spider servants which can be gained by eating her heart. A great way to consolidate absolute power, if you can kill her.