It's a little bit unclear, since there hasn't been much "spell-damage only" gear for a while, in that gear either has plus to some particular school of magic (like fire), +healing, or +damage and healing, which affects all schools. Additionally, since patch 2.3, +healing gear also grants one third of its value as +damage. However, what I think Kalgan's saying here is that they want there to just be one spellpower stat that drives both +damage and +healing, which is another step in that same direction. That would be super-cool.
Here's why: currently, as a priest, I need to collect two full sets of gear: my healing set, and my damage set. Obviously I can't heal mobs to death, so if I want to do dailies, grind rep, or even respec shadow for some serious pwnage, I need to take off my healy stuff and slap on the power items. All the classes that can heal, and some that can't, have similar issues. But if there was, hypothetically, one unified spellpower stat, channeled by talents to boost either +damage or +healing, this would not longer be the case.
Let's take, as an example, a staff with +100 Unified Spell Power (USP), and the Priest class. For the purposes of this demo USP works the same way as +damage and healing works now. Maybe in the Holy tree there's a talent like "An additional 300% of your USP is applied as +healing," which would mean I'd end up with +400 healing from the staff. Now in the Shadow tree, there could be a talent that says "An additional 100% of your USP is applied as +shadow damage," which would give me +200 shadow damage from the staff. The key point here is that USP still works when I don't have talents, which gives me some ability to do damage even if I'm not specced for it.
This could also be useful for classes that can do multiple types of damage, like mages. Currently, +fire damage (for instance) is cheaper in terms of itemization points that just +damage and healing, so an item of the same level can have more +fire damage than it could +damage and healing. So imagine a fire talent that made an additional 100% of your USP apply as +damage, and 30% more apply as +fire damage.
Of course, we don't want gear to become overly homogenized. One can easily imagine a fully unified stat system, where items possessed only an armor class and a +power stat, which boosts various stats for various classes (tanks get more armor, melee DPS gets more AP, and so forth). This would quickly get boring. However, USP doesn't go to far in this direction, in my opinion, and it does have the significant benefits of easing off-spec set construction and reducing the frequency with which unwanted gear drops (I recently took my rogue to a Karazhan raid instead of my priest, only to see the lovely Ritssyn's Lost Pendant sharded for lack of warlocks and priests). There will be more competition per piece of gear, but the accessible pool of gear for any given character should expand to counter this.
They could also do a similar system – and this is more in line with what Kalgan actually said – by keeping stats the way they are and just giving talents to affect them. There was a Shadow Priest talent in the alpha called Growing Pains that worked like this – converting +healing to +damage – though it has been removed in later alpha builds. So maybe you have a talent like "50% of your +healing is also applied as +damage", and one like "150% of your +damage is also applied as +healing." I don't like this approach as much, because it's basically a more cumbersome way of implementing USP, but it could work.
So let's suppose either USP or simply talents to reapply +healing as +damage and vice versa are implemented. Having to respec to properly DPS is still a bit inconvenient, not to mention that it can get expensive. This is where another thing the devs have been mentioning for Wrath comes into play: some sort of smoother respec process (unless I'm just imagining this; I can't seem to find any references or backlinks, but I could swear they mentioned something of the sort). My dream implementation would be as follows: you can have your current talent spec and one saved spec. You can switch between them at any innkeeper, for a reduced cost (maybe half-price). If you want to use a different spec, you still have to go back to your class trainer and pay full price.
Combine that with a USP stat, and it start to become much easier for people who want to play off-specs. After all, damage classes rarely have to respec or, in most cases, even swap gear to grind, do 5-mans, or raid – why should a healer or a tank?
Do bear in mind that this is pieced together from rumors, a sketchy interview quote, and blue-sky speculation. However, the groundwork for a USP stat has been laid; let me recap the evidence:
- Patch 2.3's implementation of a one-third damage-to-healing conversion
- The Growing Pains talent from the alpha (which has been removed)
- Blizzard have said they're trying to unify itemization in some other areas; for instance, Ret paladins are going to share gear with DPS warriors, and Death Knights will also share gear with DPS warriors if they're DPS-specced (with talents to convert AP to spell power).
- Primarily, of course, the thing that makes me think they might be working on USP or at least more robust +damage/+healing conversion is the Kalgan quote mentioned at the beginning of this article.
So I feel confident that they're at least moving in this direction, even if there is no intention to implement anything as radical as USP (though I think USP would be a great solution to item versatility and off-spec difficulty concerns).
Update: DeathKnight.info is also reporting on this, and they have some item screenshots from the alpha compared with from the live game, with very interesting numbers.