-Well, if this is just only about high elf lore of course the discussion would be different, but we are discussing playable characters here, of course HE storylines is something that some people wants, but that's a side of this.
I stated many times that VE being BE feels insulting for somebody like me that played BE and other horde characters and don't play alliance as much or at all. But i would be fine with them if they were alliance HE infused with void in the first place (being it for the most reasonable reasons Blizzard could provide), and i would totally accept a compromise of some former HE being transformed into VE, that would be end of discussion for me here, it would be an spicy pill to take as some of them would still be BE, but the alliance could at least play something that lorewise are their allied thalassians that weren't ever horde or BE, i would prefer much the pure concept of the HE allied race instead of that little pick, at least it would not feel as bad as VE for people that feel like me and it would be very natural by itself.
And by being natural is what some people means in a contrary way when pointing to something as an asspull, it's just and allegory for it feeling forced, there is a pretext for HE that ever were there so it doesn't feel that way.
-The looks of a race aren't all, it's just a way to make them feel different, and this is the point where HE supporters really enters in muddy territory, because we know that lorewise they make sense, but lore itself doesn't hold enought for an allied race as Blizzard points out.
Some things were discussed about the looks, would they have new customisation options? of course, every new addition does have it, but what kind of customisation then? i'm not even going to say blue eyes because that's something BE should have by now alongside yellow-lighted and green being unique to them, and by now we know that blue eyes are just default as BE green eyes were for so long.
Apart that, there was a discussion about giving them a new skeleton/animations, and anti HE stated that it would be unnatural, and i agree, even giving them just a slightly different idle would not be right.
So then, the most popular choice were the tattoos/warpaint, as not all armor covers all the body, you could show some of them to give somekind of visual information, but something as tattoos/warpaint aren't that effective at all just because that surely would be an optional thing just as other tattoos/warpaints are.
But then we have something that difficultly hides, the ears, and some people here stated that giving special kind of trinkets for the hair/ears (such as feathers or jewelry made of wood or something distinguishable) could be a nice visual information, as we currently can see, nowadays we could still miss a VE from a BE even in close distances in certain situations, not even full armor, in a HE that would be more difficult adding that jewelry are, as other things, optional.
Then we have the Pandaren situation, we currently have the exact same race in the two factions with the exact same customisation options, and not much happened coming from that. Some argued that Pandaren being neutral killed their lore development, but surely they were not talking about how they look, so that would not apply to HE and BE, so they would not come from the same starting point in current lore, but they would have their clear differences, both of them even have places they can call home unlike Pandaren that doesn't seems to be returning to their island or setting locations (that's kind of Blizzard's fault), we have a precedent where nothing disastrous happened with having the same race in the two factions, and with HE, they would only not just be thalassians, but thalassians with their own way apart from BE, with their (even being little) own foundations out there in the world.
-As you can see the muddy part comes with looks, because that is what pull HE apart from being an allied race, and it's just that, just that detail that separates what we can play with what is in the lore, a VE is not a replacement just because it's ties with void and BE themes, being the void the un-apartable thing while the BE thing is the most subtle, but tied to VE, that's why i made the comparison between Mag'har and VE, you can pretend succesfully that you are from Outland or an ex-Garrosh sympathiser in the form of a dragonmaw orc because the AU draenor theme is not tied to Mag'har (That doesn't mean i like the idea of the whole AU Mah'gar...), while the void theme of VE not only separates them from HE, but have it's ties with exiled BE that currently doesn't seems to bend.
It's all in Blizzard's hands, and until now we didn't got a positive response about the matter, and definitely not an ultimatum.
Sorry if it was too long, there's much i would add, i just wanted to express what i got from participating in the HE discussion since two months, and playing wow since 7 or 8 years.