If you only skimmed over the patch notes for Warlords of Draenor, you may have missed (or just not cared about) the changes to hunter Weapon Damage and Attack Power.
One important part, is to make balancing between specs/classes easier on Blizzard, they're making all primary abilities (agility, strength, intellect) give you one Attack Power. This shouldn't matter too much in the long run, as they'll still be trying to make each class capable of a similar amount of dps ("trying") relative to each other. If we were still going to have primary stats on gems, it would have a large effect on our gemming strat, but since that is not the case, the agility change won't affect us other than in a few unique places.
The other major change, is that Attack Power will have a much more increased effect on Weapon Damage. Previously for every 14 AP you would gain 1 weapon dps, now we're going to see an increase of one weapon dps for every 3.5 AP. That's four times as much weapon damage from Attack Power. To counter this, they're going to give weapon damage a 20% nerf, relative to the stat squish.
What that means is where previously AP added relatively little to shots like Aimed Shot, Power Shot or Barrage, they'll now scale much more closely with increased Agility. At the same time, unless Blizzard finds another way to buff them (which I'm confident they will) abilities that don't have a weapon damage component (like Glaive Toss or Kill Command) will be less powerful (compared to shots that scale with Weapon Damage), since there will be less Attack Power from Agility (again, we'll of course have to wait and see how they balance this before we bother making any changes to our priority systems).
This is great news for MM huntering mostly, since MM's primary damage dealing abilities are % weapon damage shots. Where as during this past tier, MM wasn't really viable in PvE until you had a current tier weapon; if you have really bad luck, and get most of your other gear before you see a bow/gun/xbow drop in WoD, you'll still be able to play MM, because of this change to AP and weapon damage.
Of course blizzard will adjust and balance the abilities; they aren't going to let, for example, Kill Command be less powerful than arcane shot. Still, there's no way they can give them the exact same relative value, so we'll need to spend a lot of times at the target dummies when the WoD beta begins, figuring out what our new priority is going to be.
Another side of this is currently, when your Agility procs are active, you don't really want to use your abilities that rely primarily on weapon damage if there's an ability that scales with Attack Power available (which is generally true for other reasons we won't get into here), because your pure attack power abilities will scale better, and be a better use of your GCD. In WoD it seems that won't as much be the case, because the Weapon Damage Abilities will scale significantly with AP as well. Again, this is mostly important for MM hunters (because Chim Shot is a weapon damage based ability), but it will still be something to think about for SV and BM hunters.
Let's look at an example:
The arcane shot formula currently looks like this: Damage=(1.25*(WD+(.2RAP))+3289
Currently, here's how my Arcane shot holds up with some various Agility levels (note these are all hits, no crits, and the damage done is an average of 100 shots at each agi level).
I imagine that's pretty similar to the results anyone would get. And if you use my formula based on an average Weapon Damage of 36156.21, I get pretty close to each one of these.
The new formula, according to the patch notes will be: Damage=1.25*(.8WD+(.7AP))+3289
If we disregard the stat squish (which should be fine because everything is supposed to be relatively the same), we can use the new formula by simply doing our own nerf of WD by 20%, and reducing the benefit of Agi to only +1AP Here are our new results:
What you're seeing is at lower AP levels Arcane shot is going to be lower than it is now, because Weapon Damage won't be as high as it is now (relatively). But as your AP goes up, the shot will scale even more.
It should be very interesting going forward (well, interesting if you, like me, really love spreadsheets). Should keep the theorycrafters busy for quite some time.