We know that the Galakras mount is the meta, the Kor'kron Wolf is the Ahead of the Curve mount, the Skeletal Warhorse and the Nightsaber seem to be new arena/battleground mounts-- "Vicious" prefix?-- and the goblin shredder is the Sky Golem.
So what the heck is the Garrosh Heroic mount?
This icon showed up today:
It's titled "ability_mount_ironjuggernautmount".
Seems like a distinct possibility? I can't see from the encounter journal any indication that we mount the Juggernaut in combat like Flame Leviathan.