Alleria is unique because of her unique nature and the unique method by which she came by her powers. But I consider her a 'High Elf' only in the sense I consider all Void Elves as high elves, as Ion Hazzikostas described them, as 'another flavour of High Elf'. Void Elves are High Elves, but a variant. The blueberry icecream to the vanilla ice cream. The Samsung galaxy S10e to the S10.
There is a difference that is fundamental to making a Void Elf, a Void Elf.
The process that transformed Void Elves was being bombarded by void energies. This provoked a skin tone shift. The gameplay rationale for why it did this is not hard to figure out given Blizzard employed skin tone shifts on multiple allied races. It was to accentuate the differences between the allied race and the parent it was based off. Blue to purple skin tones are thematically appropriate for a race built on the theme of the void.
Unlike the addition of the High Elven exiles as a distinct allied race which seems to have been comprehensively ruled out, Holinka's comments at Blizzcon 2018 shows that high elf like customization is possible on Void Elves. But possible does not mean guaranteed.
I am opposed to Void Elves receiving high elf like customization as it undermines one of the key aesthetic differences between Void Elves and Blood/High Elves. I don't think it is fair to try and turn Void Elves into ersatz tradition high elves. They can never be that. While it is perfectly possible to roleplay a Void Elf who used to be a High Elf exile, it is impossible to roleplay a Void Elf as if they never became a Void Elf and remained a High Elf. It is still a Void Elf. It is always going to be the variant and roleplayers are free to have any story they want for their toon so long as it is consistent with the origin of the character.
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I don't particularly like betas, I prefer to keep as much content fresh as I possibly can. Should I get in all I will likely do is mess around with the new customization options and see how the class unpruning is going.
In regards to the desire for high elves as a distinct allied race, every individual has their own rationale for wanting them. Some probably genuinely do want them for lore based reasons. But my experience has shown that the majority are in it for the aesthetics.