11 new pets to collect
Here's a (temporary) list of the new pets coming in 7.2.
Note that the Death Knight and Monk companions will not be available at the start of 7.2. Gaining access to these pets on the vendor will require an 11 week campaign which unlocks the class mount quests. More information on the new class pets can be found here.
A new toy
Similar to the DK and Monk pet rewards, Mages will be able to unlock a toy that allows battle pets (that normally wouldn't follow players into the air) to fly alongside players.
3 new WQ trainers
These trainers can be found on the new zone, The Broken Shore. They're unlocked after completing the Broken Shore introduction scenario and quests. More information on their teams here. At this time it doesn't look like they will count toward Family Familiar.
Pet Battle Dungeon
If you're level 110 and have at least ONE max level pet (but it's recommended you bring along 3 or more), head over to Breanni's shop in Dalaran (Broken Isles).
A new quest will send you to investigate a mystery in the Wailing Caverns. Completing and turning in this quest will unlock a weekly quest of the same nature, except it's Pet Battle challenge-mode time. For a detailed rundown of the Pet Battle Dungeon scenario, see this blog post.
Similar to the Celestial Tournament, the challenge version of the Pet Battle Dungeon requires at least 15 max level pets, and you cannot heal or revive your pets while inside the scenario.
The challenge-mode weekly quest rewards a bag that drops quite a few Pet Charms, and has a chance to drop one of three new pets (two of which were discovered to be color changers!).
There's also an achievement tied to completing the challenge version of the Pet Battle Dungeon, Pet Battle Challenge: Wailing Caverns, that rewards a new pet.
Did I miss anything? Please let me know if there's pet/Pet Battle content that I've overlooked. :)
I'm pretty excited about 7.2, if not somewhat (or very, heh) overwhelmed and anxious. So much to do, so little time.
I would have preferred a longer period between the announcement of the release date and the actual release date itself...but *shrug* what can you do?
Can't wait to collect some new pets!