Have you beta testers seen this? Currently I believe the keybinding defaults to none so you have manually bind it. However it brings up the journal and shows a whole host of grayed out pets.
And there are a LOT.
Just to give you an idea, my character has 163 companions on one character. I have rare pets from holidays on other toons that I wasnt lucky with on main, and I have alliance pets. All in all, I have 177...
OUT OF 500. (BTW yes you can summon alliance pets on horde

I noticed there were some oddities in the list. It had Alliance Balloon for me as both a pet I have (I have it on my ally toon I transferred over) and a pet missing. However it did not show me missing albino snake. So some of the 363 I am missing may be overlap.
There are a few test pets, a lot of generic pets and even some named ones. If this goes live at even 1/2 of this list, I am going to be busy FOREVER