I would agree with you and say that we very probably do. But, some people in this thread are so determined to reject that notion - in the hopes that they can have a second playable Thalassian option on the Alliance - that they say that unless there is an explicit example of a high elf going through a void elf transformation in real time in-game, then it just hasn't happened yet and is probably impossible.
It wouldn't be erasing high elves. It would be incorporating them into the fold of the Ren'dorei. The void elves would have within their ranks elves who "never abandoned the Alliance", elves who never "went Horde" and were never "corrupted by Fel". And people could play as one of these elves with the new starting experience in Shadowlands (and retroactively think of their existing characters that way).
After all, many high elf supporters within this thread have said that "it's not about aesthetics", it's about "allegiance", "loyalty to their friends and not blind loyalty to their race" and that they "don't just want blood elves with blue eyes on the Alliance".
Surely, for people like that, playing a void elf who was a member of the Silver Covenant wouldn't be a problem, would it? If those same people said it would be a problem, then they're proving the sceptics' point that these people do just want a near carbon copy of Horde race on the Alliance with a slight eye tweak.