Maybe untamed has something to do with the dueling we saw in the trailer? Just a possibility. Maybe weather magic falls into this category?
I agree practical will probably be used for more mundane tasks like fixing objects or cleaning.
Mischief of course is going to involve pranks such as booby trapping objects or making a sim lose their memory (I hope this ties into the mischief skill somehow).
Alchemy, I wonder if this will be the same as brewing potions like in the trailer, or if it's another skill we haven't seen yet.
I'm honestly glad at the variety of magic, as it allows us to create a range of different types of spellcasters for our stories. If i really wanted to I could make an elf/fairy who specializes in mischief magic, or an earthy witch who mainly uses practical magic. A wizard in a tall tower (please include spiral stairs, please!) who concentrates of perfecting his alchemy skill, or (most likely for me) an ambitious spellcaster determined to master all four.
I'm so excited to explore this pack and I can't wait until September 10th!