Elune is a true deity. She is the polar opposite of a Void Lord. I think that Elune (Mu'sha) represents/is an extension of the feminine half of the all-binding spirit energy of the cosmic primordial sea of Light (what the Tauren call the "Earth Mother) that predated the known universe (the male half being An'she). It seems that her influence is shown in not one, not two, but THREE cosmic forces in the Great Dark: Light (Holy), Life (Sun/Moon), and Order (Stars). These are what I call "Celestial" magic (closer to spirit), where the forces of Disorder, Death, and Shadow are already known as "Sacrificial" magic (closer to decay). She has connections to both the Titans and the Naaru, and the evidence is everywhere!
Out of the 5 Pillars of Creation made by the Titans, the Tears of Elune is the only Pillar not named after a Titan. It could have been called the Tears of Eonar and its purpose would have fulfilled the same role, but it wasn't. We even see the planet that Eonar's spirit is residing on is called "Elunaria"
https://wow.gamepedia.com/Elunaria
Cementing her connection to the Naaru is Light's Heart reacting to the Tears of Elune. While this is still conjecture, it pretty much confirms her involvement in the creation of the Prime Naaru. She even has a priesthood that wields holy magic in her name.
Elune communicated to the Dark Trolls that settled along the Well of Eternity, a body of water steeped in arcane energy, that was made by the Titans. The moonwells that are used by both druids and priests are hallowed repositories of the Well of Eternity. They seemingly use a combination of Light, Life, and Arcane magic as a part of their very nature.
https://wow.gamepedia.com/Moonwell
The Moonkin/Wildkin/Ownkin are creatures that have very close connections to Elune. Balance druids transform into these creatures to gain more astral power, achieving a "balance" of Nature and Arcane magics from the Light of the Sun and the Moon.
I see Elune as being a deity that's closer to mortals and reality than her male counterpart, An'she (or whatever his actual name is... probably something related to the sun like Sol... or Solmir?... yes... that works). Anyways, she's the light in the -midst- of darkness. She wants to protect Azeroth from falling to the Void, so she exerts her influence not the through the direct light of the star itself (An'she), but a reflection of that light from the moon. She gives us balance and hope in the scary, dark night that would grip us in fear. Perhaps An'she might end up being our penultimate enemy before the Void Lords. I know players are itching to fight a faction of fanatical Naaru that want us obedient and stagnant in our love of their Holy Light. Perhaps An'she is completely blinded by the eternal conflict between Light and Void and only knows this conflict above all others. Maybe as players we'll have to deal with an antagonistic version of the Army of the Light and ultimately we'll prove ourselves to An'shee similar to how we prove our worth to Odyn. An'she might see us as beings that will ultimately help the Void Lords, but we prove to him otherwise.
Anyways, that's my head-canon. What do you think of my hypothesis about the true nature of Mu'sha/Elune, as well as An'shee being a possibly enemy down the line?