Wow, you guys are so afraid of change and are so negative, that someone proposes something new and out of the ordinary and half of you shoot it down.
Anyways, I have a few things to say (mostly from a rogue PoV) about BM compared to survival.
1. As Hurrx said, Surv burst is way more predictable. As a NE rogue I can often shadowmeld explosive shots to absorb that burst but I can't do the same with BM.
2. You can LoS a surv hunter which pretty much takes his damage to zero, but a BM hunter's pet can still be on you if you LoS and can kill you quite easily if you have already lost health.
3. Focusing on a BM hunter's pet means less focusing on a player less than you would normally do, allowing the hunter himself to do more damage regardless of your attempts to kill his pet. Even if you do kill his pet, if the pet gets an intimidation/kill command off before he dies, then it's fine because it's skills are on CD anyways...you just wasted 10 seconds killing a pet with no stun (cuz stun will be on CD).
4. Surv hunters are so popular that every time you see one, you think it's given that he's survival. A hunter being BM will give him the advantage of surprise. When I choose how I structure my attacks and CDs on hunters, I think about the hunter being surv, and having disengage, scatter shot, and concussive shot. I structure my attacks so that I can get through those 3 skills. However, if he has a stun, that's an additional skill I wouldn't normally be thinking about counter-acting (unless I knew he was BM beforehand), and even if I did, that would mean 4 skills I would have to think about getting through in order to kill the hunter.
5. Usually CC'ing a surv hunter stops ALL of his damage output (for example, if I gouge a hunter I will take no damage as his pet won't do much to me, and the hunter himself is incapacitated). However, if I was to CC a BM hunter (let's say I gouge him or a mage poly's him), there is still considerable damage output from his pet.
Anyways, that's all I can think of for right now. BM hunters sound like fun and it's also something new from the everyday OP surv hunter.
I'm pretty sure a BM and surv hunter would be a viable comp when talking of hunters on a premade team, as opposed to 2x surv hunter.
In the end, I guess it really comes down to skill. I'm pretty a sure a well played BM hunter could surpass a surv hunter.