Based off of the dressing room, the Nightborne metal chin thing and the Void Elf giant collar are part of their chest pieces. I hope that's a glitch on your part or Blizzard's files because I'm going to be rather pissed if I can't use those without some ugly chin cap on my Nightborne or a giant collar clipping through my Void Elf's long hair.
Ah yes, because what Silithid mounts really needed was even more specific limitations.
I really hope they move the Void Elve "Wings" to be connected to the cloak socket rather than chest. It would really open up transmog options while allowing us to keep them, and help them become iconic to the class.