I would be all for it but i'm not sure it's very lore friendly.
But they've bent the lore before in the past. If they can ban spells why not make some new ones?
Well, there was a few shapeshifting spells in Daggerfall, but they didn't work. Personally, if it's there, I would like it be only taught by a select few, and by select few I mean the coven witches. In addition, you REALLY need to be on their good side before they'll reveal their secrets to someone, especially if you're a male.