Well, with the new pet minimum level options and all the pet talent trees, yeah, maybe they are rethinking the idea of restricting us to just 3 active pets. It will add to Hunter versatility to have multiple pet types.
What I want is the multiple pet whistle. I can summon a dozen different mounts. Warlocks can summon a bunch of different demons. Yet Hunters have to go to a stable master to swap out pets? Stupid. Allow me to 'call' a given pet, have a 1 minute call time, whatever. Maybe a stable master opens a portal for my pet to come through and I have to pay for the summon service, again, whatever. Let me call any pet from the stable.
With 4-5 stable slots I can have a couple of RAID pets, use against physical, resistant, ranged, etc. A PvP pet. A BG pet. A solo pet.
Suddenly, a whole plethora of options open for Hunters. It would increase our usefulness a bunch of times over and make parties want to have a Hunter in them.
I have been okay thus far with just re-specc'ing one pet. Now with the immediate 5 levels below me bit, I will look at other pets. The talent trees make it so I will actively seek them out for specific uses. Increased stable slots, bonus! Ability to summon any pet I need for a situation I will be in: true awesomeness.