Dude, Nightborne has as much to do with NE as BElves do. In fact, NB are much (culture and ideology-wise) relatable to blood elves.
unless you mean physical appearance.
Makes perfect sense that they'd either stay neutral, or join horde.
I'm not particulary interested in Velves (even though they have a lot of great customization options), because they seem too edgelord-y for me, much like Demon Hunters do. Also, I'm not against new lore development, but as a new sub-race, they appeared out of nowhere, literally. The best way to introduce them would be letting they slowly appear through a period of time, much like Nightborne or Highmountain, so we can get to know them.
I'd much prefer if blizzard worked with an already existing subrace option. High elves are there for ever. Yes, they are physically identical to Blood Elves, but you could add some new hair and skin shades to make up for that. (also lore reasons why high elves aren't a race because of diminished numbers is bogus if you see Velves.)
If they were so keen in adding a void-themed race, why not just put in Ethereals?! Locus Walker is already a kind of important NPC, and could easily pull a leadership role there.