Shaman's Tier 16 mail armor look like the tier of a different class that would wear mail and have something to do with time.
If you look at the shoulders, that is a typical time-travel device you would see in movies like The Contact
And then they have their extra Tier within Siege of Orgrimmar:
Just a thought as the balanace in the transmog department is not very good for the mail class as they can only copy tier sets of each other (Shaman and Hunter).
While a Warrior can take items that has the exact same look as tier of a Death Knight and Paladin
Same with Mage, Warlock, Priest.
Same with Monk, Druid, Rogue.