It could be implemented a few different ways; for example, either by keeping the favorites menu in one straight list and putting a simple break between each category; or what I think would be better, pressing the favorites button pulls up a quick menu of the seven inventory categories (If you have no favorites in a category then that category doesn't appear) and clicking on or tapping the left stick (I'm playing the Xbox 360 version) pulls up a second menu to the right with everything that's favorited in it. So if I just have a few weapons and a couple potions favorited, only those two categories would populate the quick menu.
Magic spells could either be listed altogether under one Magic category, or it could display each magic class as its own category like the others. I'm not sure which of the two would be better. Maybe the latter, if they were just grouped together away from Weapons, Apparel, etc. and also displayed only when containing a favorited spell(s).
One big long alphabetical list isn't as good in practice as it maybe was in theory, and like I said its more convoluted than it should be searching in terms of alphanumerics when navigating my favorites menu for different categories of items. I would rather pull up magic spells with magic spells, armor with armor, potions with potions, and so on. I think this would do a good job of keeping the favorites menu a quicker and easier way to navigate your inventory while making it a little bit more organized and efficient to use.
Thoughts?