In the upcoming patch, expose armor will reduce armor by a percentage. Untalented its 40%, with talents it 52% armor reduction.

Is this extra armor reduction worth it to use in raiding situations? Or will the loss of hate by not being able to sunder cause Expose Armor have less application in raids? The dps gain from a 52% armor reduction seems like it would make the talent worthwhile in raids.

Not sure...I agree that the extra DPS is great, but at the same time....no sunders. It's a balance, but I suppose in end game tanking you have enough rage from being hit to just spam enough HSs and SSs to make up for it, plus the rogues / hunters can still feint / FD...Not sure on that one but I think it'd work out ok.

No, not worth it on raids because tanks will just overwrite it with sunder. It'll be fun for pvp since you whack a much larger hunk of armor off the high AC classes relative to what you did pre 1.12.

It certainly has a use in some situations, but the fact that it only lasts 30 seconds hurts that Rogue's dps.
Not sure if you MT need Sunder to keep aggro, some do.

Mobs have around 4000-5000 armor in BWL, so sunder is about the same as Expose in that instance. So it is better to use Sunder.

Also I don't know how it works with -armor abilities like CoR and Faerie Fire. I would guess that it would go after those abilities.

So, it is just a PvP skill against Shield Warriors/Pallys.