This are my ideas, wich you are probaly going to /that's overpower or /ignore :
Discipline
- Rapture: When your damage absorption spells are completely absorbed or dispelled you are instantly energized with 6% of your total mana. This effect can only occur once every 12 sec.
_ Mastery: Disipline balance "Every time you use a healing spell you increase the potency of your following absorption or damage spells by 10% and vice versa, it accumulates a maximun of 2 times, lasts 10 sec, the same balance can't happen for 6 sec after activated. Each point of mastery increases the amount increased by 2%"
Shadow
_ Psichic Horror and Silence exchange positions in the talent tree
_ Improved Psychic Scream changes to Psychologial studies/dark thoughts: Reduces the cooldown of your fear and horror spells by 15%
_Shadow Orbs "You have a 10% chance for your Shadow Word: Pain and Mind Flay spells to grant you a Shadow Orb each time they deal damage. Casting your Mind Blast or Mind Spike spell consumes all Shadow Orbs, increasing your Shadow damage by 10% for 15 sec. You can have up to a maximum of 3 orbs."
Discipline works on discipline and control the body, Holy works on the spirit. As Holy has a balance mechanchinc to "work on the body by the spirit healing" , Discipline should improove their "work in the spirit by disciplining the body". As a result of his training a Holy priest can reach diferent states of healing depending the situation and leaves energy when it heals, Dicipline could swich their actuate "position" quickly to reach and transmit tranquility (what I'm suggesting) and reduce the weakened soul efect (current ability).
Sorry for make you waste your time reading this madness.