When I first saw the celestials in the opening of the Vale of Eternal Blossoms, I told myself "Hey, wouldn't it be neat if we could tame that?"
It could be a hunter only quest line such as the Warlocks Green Fire quest. You find a celestial object in a random location in Pandaria and take it to Lorewalker Cho to start your quest. The final stage includes fighting Xuen/Niuzao/Red Crane/Jade Serpent and then taming it once its down to low hp, similar to Deth'Tilac/Spirit Porcupines.
The celestials would have a massive amount of hp around 40 million and need to be taken to less than 10% to tame.
You can choose which celestial you tame when you reach the final stage right before the fight. You can tame the others if/when you find more celestial items around Pandaria.
Does not require Beast Master to tame and has a new pet family named "Celestial"
What do my fellow hunters think?