I think this problem can easily be solved, really. And maybe i’m hopeful but i do think it will happen, hear me out.
The High Elves are already an established Alliance race, we could argue, like the Dark iron and some other dwarven clans, they are there just not playable.
We know the actual people that want them do not care about how they look or sound or stand or dance, as long as they hold the original Quel’dorei status and beliefs.
We know the Blood Elves and rightfully so would feel sacked if the copy+paste+edit green to blue was to happen for their model. (If the Nightborne got the exact Night Elven model i wouldn’t be all that happy about it too!)
We also know 2 models using same rig also isn’t a problem with yet another race (Zandala) using the night elven model and Kul tiran the upright orc one!
My suggestion is, make them different yet stay true to their heritage to show that both these races used to be 1 at some point. My idea was, give them a different/idle/attack/cast animations as we know there is no 2 people that stand or do things in the same manner. Obviously hairstyles that are inspired by humans/night elves etc as those are the people they mingle with and obviously have taken things from (would also explain warpaint for example)
But if that still wouldn’t sit with Horde players, i personally wouldn’t mind a recolored Night Elf model as it’s really just about the High Elves and their lore and status.