Like I said - Elves seem to evolve rapidly with magic. Without the Well of Eternity/moonwells and supposedly with use of arcane magic and siphoning power from their Sunwell, the Highborne elves turned pale skinned, looking more human and becoming the High Elves. Later, they’d feed on fel energy, resulting in green eyes, and light energy, resulting in gold. And these are the more immediate effects.
Similarly, virtually every Night Elf mage is from a separate sect that aren’t quite Night Elves. By default this group should have looked different from Ashenvale/Darkshore Night Elves, whom have lived in close proximity to a manufactured well of eternity (Thanks, Illidan) and practiced almost exclusively nature magic. Priestly magic is… arguably up to it’s source, as Tyrande doesn’t wield what appears to be light magic when she calls upon Elune.
Azshara wasn’t even under a perma-night dome shield feeding off a nightwell and she’s ridiculously deep blue skinned. Is that the effect of extreme arcane power? The influence of the Well of Eternity? Both?
Then we get to reference the Void Elves, turned very blue and pale with tentacles growing from their hair simply for harnessing void energy, practically living and breathing in it even. That had to happen rather quickly relatively speaking. Within the last 30-ish years in-lore, tops.
Blizzard has the opportunity to lay out some lore regarding how magic influences the appearance of elves. Really, what they say goes. And as far as I can tell, the Elves of Feralas (where most NE mages originate from if I recall correctly) were quite a distance from the fake Well of Eternity for thousands of years, like the High/Blood Elves, but lacked a Sunwell, unlike the High/Blood Elves. How the Elves of Feralas turned out is up to Blizzard, but I’m willing to bet they’ll be the basis for any new cosmetic options the NE might have.
Finally, if bodily changes happen rather fast in Elves, even the last 19 years in the Eastern Kingdoms could have had a noticeable influence on an individual Night Elf’s appearance.
You’re probably right in that NE will get more exotic, deeper hues, but I wouldn’t rule out looking more “High Elf” just yet either. Almost like they were making a call back to the early High Elf models that were really bad NE knock offs.