THis is different, we are dealing with sub-races (or, if you prefer, alt-races) now. They won't have unique skeletons/animations.
Alleria has a custom model based on blood elf model. Just like Sylvanas, Alextrasza or Ysera. Pay attention to her animations and proportions, it's essentially a modified blood elf.
I think "void" elves (which may be a temporary name, at least I hope so) will use blood elf models, but with a few differences. Kinda like a Lightforged Draenei uses a draenei model with unique custom options and skins.
If I were to guess, I'd expect:
- Share with blood elf only the lighter skin tones, but also has unique paler skin colors, maybe even white or bluish skin.
- Unique eye glow. Either bright blue like Alleria's, or purple.
- Probably will have options for tattoos, runes, body paint or void taint over their skin, kinda like Alleria's body paint. If we can choose color, it will probably be dark blue (like Alleria's), black or purple. (I think blood elves may get similar body paint, but theirs would be red, green, light blue or gold).
- Unique hair colors, like light blue, deep blue or purple.
Essentially, something like this:
(This is an alternative skin for Tyrande in HotS)
Conceptually, I imagine these void elves are an opposite to the Nightborne. The Nightborne are elves that are "dawning": closer to night elves in appearance, but to the blood elves in culture, and moving towards the blood elves. The supposed void elves are "dusking": closer to blood elves in appearance, but are moving towards the night elves. As such, their "light" (not in the sense of the holy power in-lore, just appearance) is dimming.
At least, that's how I theorize they could be.