Lots to cover here so…

GO!

Rune Strike
We don’t want Rune Strike to be a big chunk of your dps, because as I have said, it’s just not that interesting an ability. Few talents affect it. It doesn’t play off of runes or diseases, which are core mechanics to the DK class. If your dps is low (even as a tank) we will adjust that, but probably not through Rune Strike. (Source)

Icebound Fortitude
We don’t want Icebound Fortitude to be a button you use whenever it is up. It is designed to be used when burst damage is coming (in PvE or PvP) but the way it was getting used, because of the short cooldown, was to be on an awful lot of the time. That’s not really an ability in that case, it’s just giving the DKs 50% damage reduction. (Source)

Runic Power
We’re happy with runic power. Runes are the core part of the DK. Runic power was an addition to make the rune use and cooldown less monotonous and to give us another way to balance spells. Consider that Death Coil for a rune cost would either be better or worse than Blood Strike and probably used or ignored accordingly. Runic power can carve it its own niche. (Source)

Horn of Winter
We wanted to try the Horn of Winter change versus just giving DKs another version of Bloodlust, because we try to only recycle existing abilities as a last resort. (Source)

Addition of a +Defense Sigil / Runeforge
Yes. We are probably going to do both. As with everything though, there will be a trade off. If you enchant for defense, you’ll be giving up whatever else you could possibly get from the enchant.

The way we designed death knights, they are going to struggle a little more for defense than warriors and paladins. Our goal is not to make gathering defense a non-issue for them. (By contrast it was a goal to make defense a non-issue for druids.) We just think it’s a bit too hard at the moment, which is why the sigil and runeforge changes are attractive. (Source)

Developer Q&A (Source)
Rune Strike’s damage should not be nerfed, but it’s threat should be increased
This makes the ability too good in PvP, which as I said, is a problem. I predict it will be something like 150% instead of 200% weapon damage, but 150% threat.

if Icebound Fortitude is going to scale, make it scale off Res and Def
Again, this makes the ability too good in PvP if it scales of Resilience, which all serious PvP players have in abundance. In PvP you can just use it too often. In long boss fights, being able to use it often is cool. But PvP fights tend to be very short, which means you have IBF available a lot. Scaling it with def isn’t intended to force you to stack def for PvP. It allows us to tone down the damage reduction for PvP overall while still ensuring that actual tanks can use it to tank.

I think my reference to the paladin bubble threw a lot of people. Of course the abilities aren’t all that similar. What I meant was that IBF is being used too often in PvP to avoid damage. It’s just too good an ability for a class with a lot of short-cooldown abilities.

DK TPS is lower than other tanking classes
I don’t know if this is actually the case. I could believe it for Blood on multiple mobs, which is why we need to buff Blood tanking a little.

Bone Shield is fine, dont nerf it. Buff Unbreakable Armor.
Bone Shield is not fine. When the cooldown is off, DKs are too squishy. If we buff their mitigation then Bone Shield turns them into the best tanks. We do plan on buffing Frost Presence’s armor and magic mitigation to compensate for nerfing Bone Shield. Your incoming damage should be the same, just smoother. We will also likely lower the cooldown of Anti-Magic Shell a little. All of this still needs a lot of testing however.

“We need more sigils in the game. you can add tanking/dps sigils to Badge vendors.”; “Reaching def cap is harder for a DK than a Warrio/Paladin due to 1H weapons and shields having defense + enchants. Add a static -1% crit immunity to Frost Presence”
We are adding more Sigils. We will likely add a defense proc sigil too and a two-hander runeforge defense enchant. (Dual wield tanks already have lots of +defense weapons available.)

Howling Blast’s cooldown is too long and it’s damage is too little, please buff it
In the beta, we found that it was hard to get Frost knights to use both Howling Blast and Obliterate. Too often they just went with Howling Blast over and over. The numbers may have changed enough since that time that it’s no longer a problem. (Source)

make Scourge Strike equivalent to Frost Strike in that it can not be parried or dodged
Scourge Strike is one of the strongest abilities a death knight can get, so we’re not convinced it needs to be buffed. Frost Strike can’t be avoided because it competes against Death Coil, which can’t be avoided. Without the anti-avoidance, Frost death knights have trouble with threat. Unholy death knights can do strong Death Coils as well as Unholy Blight, so we don’t anticipate a problem here.

DKs will end up still going for Swordshattering once they no longer need the new Runeforge Defense enchant, which will make it just another bandaid fix.
Having a DK choose what kind of enchant most benefits them we think is actually a good thing. It’s cooler if there is a legit choice in tanking enchant. While you might “graduate” from defense enchant to parry enchant, you might also decide to keep the defense enchant and replace some of your defense gear elsewhere. But even if all you do is graduate, it’s still a gear decision players will make at some point. Bundling defense with parry would make Swordshattering even more OP.

Ebon Plaguebringer not properly stacking with multiple Unholy DKs
There are a few cases where classes or specs with the same debuff don’t provide equal benefit to everyone. While we don’t want the actual debuff to stack, we also don’t want to penalize players for not having the benefit or get into a race for who can get the debuff up first. Unfortunately it’s not a trivial problem to resolve or we already would have done so, but it is something we want to get fixed.

In the meantime, if your dps is suffering beyond what you can endure, you do have the option of going Blood or Frost. (Source)