If regarding the Aether Shop Tier 3 & 4 costumes, they are not costume pieces but costume powers giving you the appearance of a group in the game, like a Talon of Vengeance or Goldbricker or Legacy Rikti. It's like the Halloween costumes or the costume some missions put you in that changes your appearance but nothing else. The latest Tier 4 costume is a block appearance and you can see them in the Issue 28, Page 1 post.
You can seen some of the available costumes in the Aether Shop here:
https://homecoming.wiki/wiki/Prismatic_Aether_Particle_Salvage#Tier_4_-_Deluxe_Costumes
And if you want to check out the costumes, you can hop on the test server, grant yourself Prismatic Aether and buy the costumes. Or Monstrous Aether to check out the mini pets.