Literally the same reasoning applies to Stormwind Humans and Kul'Tiran Humans.
And what would happen if High elves do indeed get a new model? Angry bobwuzhere1224 will come to Ion's house and beat him up?
You still haven't explained why exactly a faction barrier makes it impossible to give a new model to an allied race in this situation. All your arguments why are still applicable to Kul'Tirans a well.
Half Elves are not a separate race as per the game's terminology, they are not separate species, like Orcs and Trolls are, they are not a separate faction, like Stormwind Humans and Kul'Tiran Humans. You are asking to create a brand new race so that people who want a different race shut up. That's all that you are doing. And this reasoning makes creation of Half-Elves simply stupid.