You can capture wild pets, you can use your current ones, you level them, teach them abilities, even special master ones and have pet battles. There are pets you can only find when conditions are right, and in certain zones. So potentially you could find a pet only when it's raining at night in Elwynn forest.
Anything aside from raiding and PvP I can do end game is a welcome addition for me.
This is why I quit WoW long ago. Literally everything implemented after BC was a distraction from the facts. PvE endgame is egregiously time-consuming and ultimately frustrating or boring. PvP endgame is a stilted crap-shoot that simply cannot be balanced.
Call me pessimistic, but I don't think pet battles are going to change that.
I actually don't think this will ever make it to live realms, kind of like the dance studio was talked up and fizzled (but is supposedly making a comeback!).
I mean honestly, this is a direct clone of the Pokemon battle system in every way. I'm sure when more details come out, there will be elements, or creature types, which represent bonuses or resistances and that as they grow stronger they grow and become new elite pets etc etc. It's just ridiculous, honestly, and I almost find it offensive. This system has been the nail in my WoW coffin, that they would even consider this, regardless of whether it is implemented.