This is a list of untameable, or tameable-but-restricted looks that were introduced in Legion. It's just a subset of the main list that focuses on Legion things.
Restricted Looks
Tameable by some players but permanently untameable by others.
Wolves
WolfDraenorRustic : only available as the
Jandvik Ripfang, which cannot be attacked/tamed after completing the quest Removing Obstacles in Jandvik, as all the NPCs become friendly.
Existing But Untameable Looks
Potentially could be set tameable.
Wolves
WorgBlue : used by the
Ebonclaw Worg in Halls of Valor.
Stags
Doe_Grey : used by the
Shieldscar Doe in Suramar.
Tameable in 7.1.5
Oxen
MuskOx_Yellow : used by the
Thunderhorn in Stormheim and
Angerhoof Bull in Halls of Valor.
Unused or Unreachable Looks
Includes looks that exist on NPCs that are in areas unreachable by Hunters.
Oxen
MuskOx_Grey
Mechanicals
MechanowolfOrange
Stags
Stag2_White : plenty of white stags in the Broken Isles but all use the older patterned model
Stag2_Green : used by Greathorn Stag in Emerald Dreamway but this is only accessible by Druids.
Doe_Green : used by Greathorn Doe in Emerald Dreamway but this is only accessible by Druids.
Wolves
WolfDraenorRusticYellow
Scorpids
FandralFireScorpion : actually used by Emberspit Scorpion in Shaman-only version of Firelands. The model is older than Legion but has only first appeared on a beast here.