If SL has confirmed anything is that achieving class and spec balance is like chasing a carrot on a stick. Blizz can polish them to the point that it's acceptable but it's never truly going to be a reality.
There will ALWAYS be a meta and there will ALWAYS be top specs and under performing specs for elitist min maxing players.
That is not a reason to avoid introducing new classes and specs, other wise it will eventually get stale without such new content. Personally I'm on the Tinker or Dragonsworn for 10.0 bandwagon. But I've also been a huge 4th spec fan since druids got the feral tree split.
So my take on 4th specs are "Paragon specs". Essentially they are like Hero Specs that your character must unlock after reaching max level via a small quest-chain to explain why you're class is learning a new combat style.
Some of these might seem a tad outlandish for their class, but that is the point. Classes are evolving and learning new ways to fight baddies and your toon is the pioneer in these new methods.
So here they are...
I do not own any of the following art and all credit goes towards their respected artists.
Priest: Inquisitor (DPS)
Uses the light to purge evil rather than healing allies. The Inquisitor priest focuses their faith to sear their foes and ignite them in righteous flames.
Mage: Chronomancy (Healing)
Utilizes various time charms and spells to reverse the wounds of their allies and prevent incoming damage.
Warlock: Blood (Healing)
Similar to Discipline Priests, Blood Warlocks are offensive healers. They siphon the blood of their enemies to rejuvenate the flesh of their comrades.
Monk: Flamedancer (Range DPS)
As taught by Chi-ji, the flamedancer monk uses the flames of hope to singe their foes.
Rogue: Dead Eye (Ranged DPS)
Dead Eye rogues use deadly accuracy to dispatch their unfortunate targets from a distance with swift and deadly shots. In addition, combat rogues are now Tanks, focusing on parrying/dodging melee attacks.
Demon Hunter: Light sworn (DPS)
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Uses the ultimate speed of raw primal light to decimate their foes in quick and blinding attacks.
Demon Hunter: Void Bound (tank)
With 2-handed weapons, Void Bound Demon Hunters protect themselves and their allies using the void’s overwhelming and consuming nature.
Hunter: Dark Ranger (DPS)
After the defeat of Sylvanas, those abandoned by her and those risen against their will in Darkshore have taken upon themselves to find a new purpose on Azeroth. They have decided to instruct hunters in their dark arts as dark guardians of the wilderness.
In addition, survival hunters are now tanks.
Shaman: Earth Warder (Tank)
Earth Warders utilize shields and earth magic to cover themselves in earthen plates. Continuously reinforcing the plates cause the shaman to temporarily turn into an earth giant.
Warrior: Gladiator (DPS)
Uses 2-Handed Weapons in conjunction with a shield. These Warriors relinquish their tanking capabilities and unleash deadly weapon attacks that can only be done when combining large weapons and unyielding shields.
Death Knight: Fleshcrafter (Healer)
These death knights utilize the necromatic powers learned from Maldraxxus itself to fortify and mend the flesh of their allies. Like Paladins and Monks, Fleshcrafter DK’s are healers that can fully utilize their ability arsenal in melee combat.
Paladin: Conviction (Range DPS)
These paladins use the light to augment ranged weapons. Using Holy ammunition, these crusaders relentlessly hunt evil monstrosities that would cause harm to innocents.