I was finally able to upgrade my garrison's Town Hall to level 3 on the beta today, and the plot for the Pet Menagerie appeared.
I can't build it yet, but the initial plot is there and NPCs have already started to populate the area. I'm not sure if this is a bug, as per LeCraft's Tweet, or if the NPCs are independent from the dailies. The pet battle dailies from my garrison are still hidden and I can't access them yet.
Squirt, the Wandering Trainer was my first visitor (she's in the small grassy circle on the left in the image above). She has three pets in tow, Deebs, Puzzle and Tyri.
Not only are these legendary (orange quality) pets, but Puzzle is especially cool. You can actually attack him outside of a battle, and when he dies, he drops his loot much like a Treasure Goblin does in D3: Reaper of Souls. Luckily (or unluckily for us since we have to battle him), he respawns almost instantly. Fun stuff! It's a shame you can't pick up his gold. :P
You can challenge Squirt to a battle, but I haven't attempted just yet since disconnects are an issue on the beta at the moment. I'm guessing that defeating her will be part of a daily objective once my Pet Menagerie is fully unlocked and built. The NPCs will probably rotate daily too, so I'll check back tomorrow to see who shows up.
A trainer wasn't the only NPC that was waiting at my Pet Menagerie - Lio the Lioness, Pet Master also resides there.
She's a vendor that sells the new leveling battle-stones, experience food, and pet-vanity items. She only accepts a new currency, Pet Charms. I'm still unsure where these will come from, but it's possible they're connected to the Pet Menagerie dailies.
I'm excited to see what happens next. When will I finally be able to fully upgrade my Pet Menagerie? Who will show up? What will the dailies consist of? What rewards are waiting for me? What are the requirements/prerequisites for the garrison pet battle dailies (if any)?
More, I must have MOAR! :P