I can't for the life of me see how Charisma would link to Fear and Charm saving throws. If anything, a high Charisma score could lead to the vanity of the character making them more susceptable to Charm, whilst fear is simply irrelevant. Charisma saving rolls should be basically about Reaction rolls from NPCs. eg. Tyrant King wants to execute the characters he has prisoner - roll a Charisma saving roll to talk him out of it.
I have no objections with doing a Castle and Crusades style 'Saving Throws' for skill rolls - where the base score is modified by Class decisions and (possibly) the Level of the character. However, the one thing 3E onwards got right was to de-finicketise the Saving Throw types into broader, more meaningful categories.
So, currently we have:
Constitution based Fortitude Saves
Dexterity based Reflex Saves
Wisdom based Will Saves.
All we need to do is add useful categories to the others:
Strength based Might rolls (for lifting heavy doors, bending bars, jumping large distances, etc)
Inteligence based Idea Saves (for when players haven't got a clue what to do next)
Charisma based Charm Saves (for dealing with tricky social encounters, and not screwing up the date because you forgot to change your pants).
Indeed, this could lead into a free-form skills system based on the Abilities in a manner not too disimilar to Unknown Armies.