There you have it, the moment the blood elves and high elves turned into two different things. He does not goes into it, but we know there's still high elves that didn't take that path, didn't rename themselves and remained in the Alliance, and thus are not covered in that speech. It's amazing that you refuse to see the obvious. High elves and blood elves are not the same thing.
High elves and blood elves are not the same thing. They share an origin, but their paths diverged ten years (in-lore time) ago.
What more need be said. Chris Metzen said 'Blood Elves are our High Elves'. Talk about ultimate word of God. And it completely proves you wrong that Blood Elves are not High Elves, as you stated earlier, when the author of the franchise's lore can contradict you.
The problem here is that you see Blood Elves and Alliance High Elves as equivalent groups. They are not. Blood Elves are not only High Elves, they are the true definition of what a High Elf is within the Warcraft universe. They have the Sunwell, the lands of Quel'thalas, the city of Silvermoon, the Magisters, the Farstriders as well as the vast majority of the population. And they conform to what the genre trope of a High Elf is expected to be.
Alliance High Elves on the other hand are a tiny population living in exile in Dalaran, whose numbers are no longer sufficient as of Legion to maintain their own district anymore. They are traitors to their people but they are not a separate race from their people, nor do they have the right to define themselves as the true heirs of the legacy of their people.
Where your quoting of Chris Metzen falls apart is where you cite the circumstances at the beginning of TBC to demonstrate how different they are. This is an example of being highly selective with your sources, because as we all know the circumstances described by Chris changed at the end of the burning crusade with the restoration of the Sunwell. The Blood Elves no longer syphon demon magics, or syphon ambient arcane energies (something reflected in game with the removal of the mana tap racial in the Wrath of the Lich King). So if that was the moment the Blood Elves and the High Elves turned into two different things, a debatable proposition in itself as the High Elves of the Alliance were as equally crippled by the addiction, then the restoration of the status quo ante erased the point of difference.
In fact, as the Shadow of the Sun proved, Blood Elves and Alliance High Elves feed on the same sunwell again. And as the Quel'Serrar questline proved, even the few remaining Alliance High Elves hold the Sunwell in reverence and still sought pilgrimage to it. Blood Elves and Alliance High Elves walk different paths politically. But that political difference is nowhere near enough to accord Alliance High Elves a superior claim to the legacy of Quel'thalas.
Different eye colour is obvious, most Alliance High Elves have blue eyes and most Blood Elves have green eyes. Golden eyes prove eye colour is mutable though, which is why some of us hope to see a blue eyed option available on Blood Elves, which Ion may have hinted at with his 'contact lenses' promise.
Their different relationship to magic? Hard to know what that means, both groups are addicted to magic and both sate it via the Sunwell and both still exalt the Sunwell given the pilgrimages. It is the fundamental, and I would say defining, characteristic of the entire high elf race. Given we cannot ask him to clarify it, we can only extrapolate based on our knowledge. Frankly, the majority of the Alliance High Elves are likely former Farstriders. Either part of the small group that defied Anasterian to follow Alleria through the Dark Portal (who likely returned to Azeroth once the Outland campaign is done), or those in the wildnerness who refused Illidan's teachings and founded the lodges, and who then later congregated in Dalaran under Veressa. An addiction to magic does not immediately equate to a magic user after all, so I would put forward the theory that what Ion meant was that the Alliance High Elves, as primarily Hunters, don't venerate magic as much and may regard the addiction as a burden. The Silver Covenant after all joined the Hunter class hall in Legion. Blood Elven society on the other hand, and likely the entire Kingdom prior to the fall, venerates and exalts magic. They glory in it, they have always gloried in it and they will continue to glory in it.
Perhaps it is not the Blood Elves' culture who has changed? Maybe it is the Alliance High Elves who are rejecting the magic that has always formed the core of their people's society even as they are assimilated into human society. Which of course, emphasises yet again how the Blood Elves are the true High Elves of the Warcraft universe.
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Then they wouldn't be High Elves. As long as there is a physical change to accompany this, it would not infringe on the thematic or aesthetic integrity of the Horde or the Blood Elves. This is actually a good idea with one drawback.
This is exactly what they did with Void Elves. Find an external energy source, apply it to a group of elves to provoke a physical and thematic differentiation from the Blood Elves, and add it to the Alliance.
In other words, what you are suggesting is exactly what they have already done and for a small, vocal group of players it wasn't enough. Why would this suggestion work?
More to the point, whilst Blizzard's writing isn't exactly stellar, I think even they would baulk at the idea of another random group of Elves encountering yet another magical artifact and undergoing yet another unique transformation.