: Arcane: Make the spec into a Monk-like melee spec utilizing the Runemaster RPG class concept. They can use a Ranged/melee hybrid concept similar to Mistweaver Monks.
Fire: Tie it more closely with Blood Mages from WC3, making the Flamestrike ability the core ability of the spec. Introduce the Phoenix as a permanent pet that can die and rebirth itself over and over during the fight.
Frost: Frost can largely stay the same.
: Beastmaster: This spec can largely stay the same. Perhaps have a stronger tie in with the pets, giving the Hunter new abilities based on the pet active at the time. Also make it THE ONLY HUNTER SPEC THAT CAN USE A PET.
Marksmanship: Make it the pet-less archer spec it was meant to be.
Survival: Survival should be based more on explosions, traps, camouflage, tracking, and killing. Kind of like a sniper, or a terrorist.
: Assassination: Focus on poisons, and potentially make it the only spec that uses poisons. Have the poisons do more than just cause nature damage over time. Make them also cause status effects. Also you can give this spec the ability to throw poison at a target with daggers, or even the potions themselves.
Combat: Melee/Ranged hybrid. VERY similar to the Demon Hunter class from Diablo 3. Allow them to equip crossbows/bows/guns for fighting at range. If someone gets dumb enough to want to fight close, combat rogues should be deadly in melee range as well.
Subtly: Make them masters of illusion and shadow. No different than Ninjas or spies. Their attacks should be devastating, and be able to quickly and swiftly dispatch opponents. Warden abilities like Shadow Strike and Spirit of Vengeance can be used in this spec if necessary.