Mount Pet: Hunters as Main Tanks

Thesis
Hunters should have a main tanking ability.  Hunters should be able to queue as a tank and do it well.  Right now we obviously don't have the ability.  We can do extreme solo'ng and can tank content that we over-gear (e.g.- 5man heroics and lesser tier raids).  We could become tanks.  Here is how.

Mount Pet
Hunters have a non-magical ability which allows them to mount their pets.  MountPet() is both their new travel form and tanking form.  Mount pet has a two second cast time and a three minute cooldown.  Dismounting a pet only requires a global cooldown.

Tanking Abilities
While mounted, hunters lose their normal humanoid abilities, but generally gain improved versions of their pet's abilities.  The hunter and pet fight and operate as a single unit with a single health pool.  That health pool is the pet's, but if a pet dies then the hunter is stunned for five seconds.

Mounting a ferocity or cunning specialized pet is possible, but it is not a good idea to attempt tanking without a tenacity specialized pet.

All mounted pet abilities do more damage and are more effective while mounted than while unmounted.  However only tenacity abilities are improved beyond just numbers:

• Growl becomes a real taunt.
• Avoidance and Cower are proactive defensive cooldowns.
• Basic attacks generate extra [3x tank] threat.
• Charge (Tenacity) is on a shorter cooldown.
• Last Stand (Tenacity) is on a much shorter cooldown.
• Thunderstomp (Tenacity) does more damage and generates more threat.
• All Tenacity pets will have a new interrupt ability.  Pets with existing interrupt abilities (e.g.- the Special Ability, Pummel) will have two.
• Special abilities are slightly improved.
• Bonus abilities are slightly improved.
• Exotic abilities are slightly improved.
• Movement speed is greatly improved. 
• Pet health, armor, and dodge values are recalculated at a higher value than just the normal values inherited from the hunter.  Hunter gear and buffs do apply here, but don't double-dip.
• Additional abilities may be also available for flavor and variety.  Being able to summon a stampede of the same pet would be a useful cooldown.  Dire-beast might also be useful but have a suicidal taunt effect.

Tanking UI
Abilities on a cast bar are arranged once for tenacity pets, once for cunning pets, and once for ferocity pets.  If a mounted pet does not have an exotic ability or a bonus ability, then that button will be blank.

Items like potions and healthstones may be plausible.  But generally all hunter abilities are not usable.

Dismounting
When the hunter dismounts, the pet's stats, abilities, and most notably health are brought back to normal levels.  Dismounting only costs a global cooldown.  The new pet current health should be established as a percentage basis from it's while-mounted health percentage.  After dismounting, threat toward the pet is not immediately removed, but fades like normal threat fades.  As the pet is much weaker this can be detrimental.  If a hunter accidentally dismounts, they may also have a problem with the three minute cooldown on the Mount Pet ability -- and if that isn't an issue -- they may have a problem with the two second cast time of Mount Pet.

New Talents and New Glyphs
These would be far too speculative an area to discuss.  But suffice it to say these would be quite fun to dream up.  All new talents should be useful whether you're tanking or not -- but certainly more useful when you are.  Many new talents could enhance Survivability.  Many new talents could enhance Beastmastery.

New Specialization?
EDITED TO ADD: I wrote this yesterday in one sitting.  Thinking about it a bit more, the model Blizzard uses to determine roles is not one of choice and assignment.  It is based on Specialization.  So it would seem that hunters would need to have one specialization which is specifically oriented around tanking.  This would not be easy to just fold under BM.  I find the word "Huntard" horrid, but it makes me think that an entirely new Specialization would be more suitable than pushing all BM hunters into a tanking role.