The following ideas are meant to fit in the imaginary 4th talent columns.
----- Level 15 -----
[all specs] Void Shift:
no mana | 1m cooldown | 30 yards range
Swaps the position of you and your enemy target. Cannot affect bosses or other units immune to disabling effects. Void Shift doesn't cause threat and instantly puts you out of combat.
+ Glyph of Void Shift (minor): a successful Void Shift also swaps the appearances of you and your enemy for 10 seconds.
----- Level 30 -----
[all specs] Winged Feet:
Movement slowing effects cannot reduce you below 75% of your movement speed.
----- Level 45 -----
[discipline] Preacher's Convinction:
Your Atonement will always heal yourself despite the atoned target is another allied unit. The healing on you will also be 100% instead of half.
[holy] Holy Concession: {must remove "Glyph of Val'kyr"}
Your Spirit of Redemption is improved by the Val'kyr form, allowing you to also move and attack. In addition, you will be even able to resurrect a corpse. Casting Resurrection is possible despite being in combat, but if successful, it instantly dismisses the Val'kyr.
[shadow] Vampiric Kiss:
Replaces your Vampiric Touch with Vampiric Kiss, a more powerful spell that fears both the target and the dispeller when dispelled and automatically jumps to the enemy that dispelled it, refreshing its duration. Vampiric Kiss will also afflict enemy units in melee range from the target.
----- Level 60 -----
[all specs] Psyfiend:
2% of base mana | 40s cooldown | 30 yards range
Summons a Psyfiend at the targeted location that cast Horror to nearby enemies, preferably those attacking you. Lasts 10 seconds.
----- Level 75 -----
[all specs] Inner Focus:
no mana | 1m cooldown
Removes any interruption and silence from you, and grants immunity to them for the next 5 seconds.
----- Level 90 -----
[discipline+holy] Absolute Devotion:
Your Prayer of Healing now affects all units within 30 yards from the target, but increases its mana cost by 20% per target healed.
[shadow] Dark Waves:
Doubles the radius of your Mind Sear
------ Level 100 -----
[discipline] Blessed Barrier:
Improves your Power Word: Barrier's spell, disallowing enemies to enter in it and granting it to absorb up to 100,000 external damage for all allied units inside it. Enemies cannot violate it only until the absorbion effect is broken.
[holy] Overloaded Lightwell:
When summoned and every 30 seconds, your Lightwell releases a Circle of Healing around itself, without triggering your cooldown.
[shadow] Twisting Dissipation:
Your Dispersion now reduces any damage taken by 99% and fully charges your shadow orbs. It will also deal X damage per second to enemies in melee range.
Let me think what do you think about them, maybe check the talent calculator to check how they fit. Share your ideas