I would argue against that heavily considering there are multiple “Quel’dorei _____” fighter NPCs and High Elf Scholar NPCs in the War Within Alpha and/or datamined and logically speaking I see no universe in which all the Alliance and Silver Covenant Helves decide to randomly join the Void when they haven’t for the past few expacs despite having the opportunity lol. Just because 2 Belf defectors who were vocally complaining about the Sin’dorei joining the Horde are now in the Velf camp doesn’t really suggest all remaining High Elves are joining the Void or the Light lol
Yes Arator is living in Silvermoon currently (their shared ancestral home lol) but he seems like he’s being set up to become some sort of Void-Light Paladin mixture with his new tattoos and his parental figures each representing the opposite ends lol
Neutral and Alliance High Elven groups and individuals have remained independent of the Void/Sunwell for a while now and I doubt they would decide to change that for literally no reason. The Void isn’t just some new aesthetic to take on lol it fundamentally alters your existence and makes every moment a possibility of being driven to madness, and they aren’t going to go join the Horde so 
What is MORE likely IMO is that Thalassian Elves all come together to defend their shared home of Quel’Thalas in Midnight and then High Elves are made an official neutral playable race via either a name tag change option or more customization options
THAT has been the common thread reiterated across stories and questlines recently, how Quel’thalas is their ultimate shared home and they want what’s best for it and would like to be able to live their freely, which sets the stage for them to all defend it together come Midnight