Blizzard will eventually add new customization options for allied races, since many people play them. When they do, pink skin tones for void elves seems like a natural addition. I can see them touching allied races towards the endgame of Shadowlands or in 10.0 if they plan to continue adding customizations in future expansion. But I can't see them just straight ignoring 10 races just because they are not core races. I know they said they have only the core races planned for Shadowlands' release, but eventually they'll run out of core races to improve.