Yep! Raiding with Leashes VI: Pets of Pandaria.New Raiding With Leashes (I think we're on #6, MoP)
Interestingly, it still doesn't answer what they're doing about ToT/Siege already having pets, as the achievement is just the first tier: MSV, HoF and ToES.
Pets are...
Stoneclaw
Wayward Spirit
Comet
Baoh-Xi
Azure Windseeker
Spirit of the Spring
Kor'thik Swarmling
Amberglow Stinger
Spawn of Garalon
Living Amber
Ravenous Prideling
I would guess the drop locations, in order, are...
The Stone Guard (MSV)
Gara'jal (MSV)
Elegon (MSV)
Will of the Emperor (MSV)
Tsulong (ToES)
Lei Shi (ToES)
Imperial Vizier Zor'lok (HoF)
This one doesn't really fit, but the list is mostly in order so.... it would seem to be Blade Lord Ta'yak
Garalon (HoF)
Amber-Shaper Un'sok (HoF)
Either Shek'zeer in HoF or Sha of Fear in ToES
There are indeed new Zandalari and Kul'tiran orphan whistles in the data!Children's Week update (new orphans and pets?).
To add, there seem to be 4 pets flagged Children's Week. Scaley (lizard?), Froglet, Beakbert (turtle) and Mr. Crabs.
As well as 3 new balloon pets from the Darkmoon Fair: Wolf, Murloc and Horse.