After re-reading A Good War Lorash tells us that in addition to being a Thalassian of the first generation, that his mother (Highborne / Thalassian) died in the invasion of the scourge! that means that she was an original highborne that was still alive a few years ago! having that in mind it would not be unusual for some current blood elves to be highborne in the past! becoming thalassian happened very fast for them as we see in the comic sunwell trilogy!
I believe that Andorel Sunsworn could be one, he is quite old so we can read in his quests and he has a lot of resentment against night elves!