It would be nice to have some sort of artifact allowing the player to put learned skills into it. It would allow you to change build in game and not lose some important skills to unlock the different spells. Maybe the artifact could be invoked? Or found somewhere in the underground world? In my humble opinion, being able to store memory data (in this case thaumaturgy skills, insight and concentration) for a mind thaumaturgist makes sense. A new spell for that would be great!