This thread is to discuss the very very very very impossiblish (Yes, I made that word up.) 4th specs from a lore point of view especially not about it going to get ever implemented, not the actual game mechanics, not how they resemble other classes and not how stupid a healing spec for mages would be in WoW.
First things first and I want to point out that I made a new thread for this to focus on the lore aspect of these new 4th spec suggestions. Every single time you look into a 4th spec suggestion thread, you will notice people fighting about the specs fitting to the WoW universe. I have not at this point thought of a 4th spec for every class and I am actually making some of this up while typing, and if this thread keeps alive I will update them with better ideas with more thinking behind them.
I will start of with mage.
Chronomage: A healer mage with abilities to protect his allies from harm by bending the fabric of time. The special and unique aspect of this spec would be spells which focus on returning the target to a state they were in a fixed time ago, instead of just healing them up.
Maybe it could be expanded towards using the light trough arcane attunement? Sounds actually weird in my own ears but give it a go if you want to expand on it.
The story behind this spec is the change of time period towards the Age of the Mortals. The bronze dragonflight is very concerned about the future of their time controlling magic. (No pun intended) They decide to bless some experts of arcane arts with their gift and knowledge, but limiting it for only to be used on allies to preserve their life.
Like pointed out the magi already have a limited power over time, but the bronze dragonflight teach them how to use it more precise, and in completely new ways.
Next up is death knight, with propably the most common suggestion - Runecaster, a healer who controls the lifeforce of enemies and allies through manipulating blood of the enemies and allies.
This spec is quite self explanatory so I will cover it very very briefly. Heal, but cause corruption. Vampiristic traits to transfer life force from enemies to friendly targets. Transfer health from an ally to another ally.
I chose the spec to be the Runecaster, since they already exist in WoW and are quite tightly knit into similar lore. They are not technically death knights,(my own additions here) but some have risen in the ranks of the Ebon Blade and started sharing their arts with fellow death knights, until it became a very common specialization.
Shaman: Earth-Warden, a specialization using mainly the element of earth to empover him/herself to endure damage. This is also a very common source of discussion so I am more interested in hearing your thoughts instead of sharing my own, but I will share my thoughts briefly.
The Earth-Wardens have been very secretive about their specialization in their arts, and they have been shunned for using shamanistic abilities in such masochistic way. It does hurt after all when a dragon claws you even though you wear some mail armor. They are the masters of earth, and posess also healing powers through the elements of water, and the wild.
I am going to stop this here and wait for your suggestions. I left the explanations very short because I rather discuss the possible additions with you instead of just writing them down for you to read.