Soo.. posting this in the pvp board because that is where it would make most of the difference....
When you are stunned, your pet is not stunned. If this is true, then I would contend: from second, if you have cast a pet spell, and you are stunned, your pet should still cast the spell. And from first, if you are stunned, you can't cast a spell so, the mechanic would stay the same. It's a very small strategic tweak, because you can never know for sure you will be stunned, but I think it would make an interesting change in the dynamic if this were implemented.