I have not seen this posted yet soo in 7.2 after you finish the mount quest you can buy the book from the stablemaster in our class hall.
Currently it requires:
-10k resources
-Maxed Titanstrike artifact
MM and SV full artifact can unlock a new color of the mount for purchase of 10k resources respectively.
Unknown if it has an ability due to it being NYI and artifact gated.
List of possible skins:
http://www.wow-petopia.com/family.php?id=feathermane
Includes:
Gryphons
Hippogryphs
Wyverns
Wolfhawks
Owlcats