I agree with this. Void High Elves really only work if they're transformed against their will (like, for instance, a faction of the Sons of Lothar captured and tortured by the Shadowguard). As it stands, there are no new Void Elves, and certainly no Quel'dorei among their number - Void Elves are a specific handful of Belf exiles half-transformed into ethereals by Prince Durzaan.
I'm not a fan of time travel (I think the last person to use time travel in fiction without it feeling like a cheap narrative shortcut was H.G. Wells), but I also don't think High Elves need their numbers justified - if Void Elves, Lightforged, Huojin, Tushui, and Bilgewater all make valid populations, Quel'dorei certainly match the criteria.
I do really like the idea of a new group in Northern Lordaeron/Greenwood, hiding in the shadow of their own captured Runestone. It would be a great way to reintroduce the WCII Helf visual palette, and a wilder, fiercer look would make sense, as these guys would have presumably spent the last decade and a half ranging the outskirts of a hostile territory.
I could imagine a group like this could really shine if the collective High Elves were forced to infiltrate some secure area in Quel'Thalas, or for reconnaissance. Say, Vereesa or Auric is taken prisoner on a pilgrimage to the Sunwell, to be used as a political bargaining chip, and these Greenwood Elves lead us through the backways and mountain paths on the edge of Quel'Thalas to rescue them.