Patch 7.1.5 has arrived! The Nighthold is open!
At least eight new mounts are available now that The Nighthold is open (LFR wings will be released at later dates) :
Yu'lei, Daughter of Jade may be purchased from the new Mists of Pandaria Timewalking vendor for 5000 Timewarped Badges. Until now it was the only colour of celestial cloud serpent to remain unavailable and it looks stunning!
A fel core hound mount, Steelbound Devourer is crafted by Blacksmithing. The plans may drop from Tichondrius in The Nighthold in at least regular mode and above, but aren't a guaranteed drop.
Remember that Looking for Raid wings of The Nighthold will be delayed some weeks.