Blood elves are our high elves - Chris Metzen
If you want to play a pale skinned, blonde elf the Horde is waiting for you - Ion Hazzikostas
Blood elves are the continuation of the high elf story - WoW
End of story, bud.
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You do realize that on many occasions a races story is progressed via one of their key characters? If Alleria is involved it means we have void elven representation. Likewise, if Alleria is involved it means that void elves will likely be relevant to some degree in Shadowlands and future expansions. Some ARs have had the main part of their story told through a zone, others have been present over the course of many expansions. You're quick to conclude that this won't be the case... and all I'm merely pointing out is that we see Alleria will be relevant (to what degree we don't know yet) in the upcoming expansion, which means there's a good chance her people will too.
Replace the word "void elf" with "high elf" in the above paragraph and see how silly you sound.