[Ranylyn]

Advantages: Lets them steal a specific spell with precision, allowing them to either get a specific one they need, or remove one that threatens them before it can be overused.

Disadvantages: Everything else. Such as how you can't steal any spells until one is used, this way.

I could see a benefit to adding a 2 SP toggle skill (1 SP to learn, 1 SP to not take a slot) to this concept, but not outright replacing the current system.