This is going to be long, sorry about that.
Over the last week or so, I’ve been trying to come up with a decent justification as to how it would be possible for a Void Elf to use Holy magic or a Lightforged Draenei to be able to use Shadow or Void magic.
Firstly I just want to say that I fully understand that the reason we as the player are able to do this is because both classes have access to the Priest class, which has Holy, Discipline and Shadow as their main specializations and Blizzard would not have made the decision to cut off specific specs to certain races, however this creates an issue for players who want to follow established lore when making characters or who value immersion, I know for me personally before this process I felt myself being pulled out of the game whenever I saw Void Elves playing Holy Priest’s or Lightforged Draenei’s playing Shadow Priests, and so this is what sparked me trying to come up with a reasonable explaination as to why it would work and/or make sense in-game, even if in the canon these things are not possible.
In the game’s lore, the Forsaken’s official religion is the Cult of Forgotten Shadows, a religion that preaches that dark energy practitioners are just as important to life as light energy practitioners and that balance must be maintained. Adherents of this faith are known as Dark Clerics or Shadow Priest’s so Shadow is a natural fit for Forsaken Priests. As we know, Forsaken are undead, and when members of the Undead come into contact with Holy magic, it burns them, this would suggest that Forsaken Priest’s should not be able to wield Holy magic, but in lore we know that they can. Specifically we know that whilst the very act of wielding Holy magic does harm the Forsaken Priest in question, there are those who choose to do it regardless, and over time the Priest will regain some signs of life, though will not fully come back to life. Keep this in mind as I change tact a bit and discuss Death Knights.
Lightforged Draenei who choose to willingly sacrifice their lives to serve Bolvar Forddragon’s new generation of Death Knight’s are able to become Undead Lightforged, that being not undead who were forged by the Light, but a Lightforged individual who was then turned to Undeath by Death magic. We would assume that based on the above information about the Undead and Holy magic that this union wouldn’t be possible, however this assumes that Death and Holy are on opposite sides of the same coin, but they’re not. Looking at the Cosmology Chart, we can see that the opposite of Death is Life, and the opposite of Light is Shadow. Therefore a union between Death and Holy would be possible, it just probably would not be a pleasant existence, but as Lightforged Draenei Death Knight are by definition those who chose this for themselves, the pain would probably be worth it for them.
Looking over to Void Elves, I initially thought this was a problem as well - we know that the Void considers Death to be its enemy, and so I thought that a Void Elf Death Knight would also not work, but I believe this works for the same reason that a Warlock using the power of the Fel against the Burning Legion works, or Shadow Priest’s fighting against the Old Gods works, as they are fighting fire with fire, so a Void Elf choosing to use the power of their “enemy” is something that I could reasonably see them making and a choice we see the other classes making as well.
Right, so I seemingly just proven that a Lightforged Shadow Priest or Void Elf Holy Priest’s shouldn’t be possible right? As the Light and Void are opposite forces, and indeed when we look at Turalyon and Alleria we see that since Turalyon is Lightforged and Alleria is infused with the Void, that the two are unable to even touch without causing a violent reaction. However I think if we look at the example of Forsaken Holy Priest’s as an example we can come up with a reasonable explanation as to how this would work.
We can assume due to the existence of Warlocks that the mortal races are aware of the concept of “fighting fire with fire”, so we can naturally assume that the Void Elves would be interested in exploring the idea of using Holy magic in their quests or Lightforged Draenei exploring the idea of using Void magic, this settles the idea of motive - i.e. why would they even want to do this in the first place.
I’ve been unable to find anywhere online that speaks as to how magic is used in game regarding if it’s the practitioner drawing upon the energy within themselves to cast magic, or if it’s them drawing upon the energy external to themselves to cast magic. If it’s internal, then I do believe that Void Elf Holy Priest’s and Lightforged Draenei Shadow Priest’s are impossible, but if it’s external then I believe a case can be made for their possibility, and indeed I believe that Forsaken Holy Priest’s lends proof to this idea as what internal Holy energy would they even be pulling from? Also the references to “calling upon the Light” also suggests its an external force.
I therefore lay forth the theory that a Void Elf who uses Holy magic does so by calling upon the Light and directing the magic where it needs to go, but that the Void Elf does not necessarily come into contact with the magic itself, or that the Void Elf is harmed by the process but is still nevertheless able to do so and might consider the endeavour worth it in order to help others. I do think Shadowform complicates matters somewhat for Lightforged Draenei Shadow Priest’s as it is literally taking up a form of… well, Shadow, but I think the logic still works if we say that the Draenei is harmed in the process.
We could also state that a Void Elf who uses Holy magic extensively may feel some of the effects of their Void infusion lessen over time, or that a Lightforged Draenei using Shadow extensively may feel some of their Light infusion lessen over time, but I’m not sure how welcome of a change this would be for Lightforged Draenei who chose to become Lightforged, but I could imagine that some Void Elves would welcome this change as their initial transformation into Void Elves was due to an accident.
All of this is to say that I think I personally can justify the existence of Void Elves Holy Priest and Lightforged Draenei Shadow Priest’s by saying that the individual would be using a “fight fire with fire” mindset and that they are harmed by the process, but are nevertheless still able to do it.
However I do understand that this is controversial and many won’t find what I’ve wrote here to be convincing, but I thought I’d put my ideas forward, but it would be nice if at some point we had some in-lore justification for this.