Something close to what you are looking for is the Wheel of time magic system. All spells are divided into talents (elementalism, Healing, illusion, etc), to be able to cast in that talent above level 0, you need to take a talent as a feat (the magical classes get bonus magic feats), also all magic is made up of 5 elements, which are availible as feats(magical classes start with one). If you have all of the elements in a spell, it lowers the required spell slot by 1, if you have some of them, its at stated level, and if you have no elements it requires a one level higher slot.
By taking different combinations playerts can personalize their spell casting abilities. An initiate with the healing talent and water affinity is very different from one with Elementalism and Fire, etc.