I am sure we have all thought about this at some point or another no matter how far we may have actually gone into the thought process, but I personally have been iterating in my head for a long time now that if Blizz was to add a 4th spec to the game the first thing they would discuss to giving Death Knights a healer option. It wouldn't be as far fetched as people think because we already have skills that allow healing.
Let me know what you guys think.
Death Knights already possess nearly infinite powers in the world of death, disease, and life. We are able to bring the dead back to life and use various resources to drain life force from friend and foe allowing us to peruse even greater power. We now discover and learn to control a new Dark Power left behind by the mighty Lich King known as the Necrotic Power, giving us the ability to summon far more powerful minions and use new forbidden spells that can now heal allies other than the great Death Knight himself.
Necrotic is an ancient power allowing Death Knights to gain access to an arsenal of powerful dark spells that can be used to invigorate his allies in various ways but at a deadly cost.
Armor Type - Plate
Main Stat - Intellect
Weapon Type - Staves, Daggers, Wands , 2H Axes, 2H Mace
Resources - Runes, Runic Power, Dark Energy
Position - Melee Healer
Mastery (Necrotic Energy) - Every time an ally is healed by a Death Knight spell while in Necrotic Presence, you have a 5% chance to reduce runic power cost of all healing spells by 25% for 5 seconds.
Along with their new Necrotic Power, Death Knights have gained access to a new type of rune called the Necro rune. Along with their standard runes, Death Knights may also take advantage of this new rune type that will allow use of various new abilities learned from the new dark necrotic power. Along with the new necro rune, Death Knights now also have Dark Energy will function similar to Holy Power for Paladins and Shards for Warlocks.
Runes - Runes will function normally. The only addition here is the Necro Rune with will allow the use of the new spells and abilities for the healer role.
Runic Power - Runic Power will act as the main resource for Necrotic Death Knights as I felt that mana wouldn't really have fit here. Runic power will be generated from a variety of ways including attack enemies as normal but also by using cool downs. Intellect from Plate will increase the effectiveness of Death Knight Spells while in Neco Aura.
Dark Energy - Over long periods of time, Dark Energy is formed inside the Death Knight from casting spells. The more Dark Energy the Death knight accumulates, the stronger the abilities that use Dark Energy become.
Necrotic Grip (3 DE) - Dark Tendrils instantly grab all friendly party or raid members places them to another spot within 15 yrds. (10m CD)
This would be a very amazing ability that would cost all 3 dark energy to use but would be useful for when raids need to move to specific spot to stack for healing or avoid damage, aka Ragnaros seeds, or Decimation on Chimeron in BWD.
VoiD Zone (3 DE) - Shifts all party of raid members within 10 yards to a different dimension for 5 seconds reducing all physical and magical damage taken by 15-20-25%.
Would basically function as a the Death Knights raid cool down just like any other healer would have.
Mystic Valkyr (3 DE) - Summons two powerful Valkyrs that fly above dealing "x-x-x" damage to all enemies within 20 yards and healing party or raid members by "x-x-x" with the lowest health. Last 30 seconds.
The abilities that were listed up above were just ideas of ways to use the Dark Energy resources. All of them are amazing abilities but only one can be used every 5 minutes, (the amount of time it takes to achieve 3 Dark Energy) meaning you have some good use of "choice" when it comes to what would be useful to your situation. Do you want to do more damage or help heal the raid, keeping in mind that the Necrotic spec is a melee healer/damage dealer.
These following abilities are samples ones that will be baseline when you spec into the Necrotic specialization as a Death Knight.
Necro Presence - While in Necrotic Presence your runic power is increased to a maximum of 300 and increases all runic power regeneration by 40%. In addition, you may now generate Dark Energy to use powerful necrotic powers. Intellect now increases effectiveness of all healing done by 25%.
Death Coil - While in Necrotic Presence, your Death Coil can now be used to heal a single ally within 30yd for "x" also putting a shield around them absorbing all incoming damage for "x". (gcd)
Defile - Creates a small pool of necrotic energy beneath the Death Knight's feet healing all targets inside of it for "x" over 10 seconds. The pool expands for each ally inside of its necrotic pool up to 15yrds. (45s cd)
Sacrifice - Fill your summoned minion with Necrotic Energy causing him to explode healing all allies within 10yrds for "x" by the Necrotic Energy. (2m cd)
Dark Siphon - Heals a friendly target by "x' (2.5s cast)
Necrotic Siphon - A large heal that heals a friendly target by "x" at the cost of 5% of your own life. (3s cast)
While I didn't begin to scratch the surface with cool ideas for spells and abilities, I'm sure you guys get the idea. While the chances of blizzard giving Death Knights the ability to heal are remote at best, I still think it could happen and is reasonable.