How do you rebalance tank DPS and have Blood DKs come out unscathed. Like, what are you guys observing exactly?
Well, at least from how a few normals have went so far, and from a few predictions as to how raids will go, our DPS does not seem to need much of a change.
I think the reason you might see Blood DKs doing massive DPS is our ability to trade off practically 80% of our survivability in order to spam damage with Blood Boil, which is WAY better than Heart Strike with 2-3+ mobs now if we have diseases spread. We can Death Strike twice (1 frost, 1 unholy each) and heal 14% and get a 14% (or so) of our health Blood Shield, wait for the runes to come back, and do it again, OR, we can hit Blood Boil four times with those 4 death runes, sacrificing a lot of survivability.
I found that when I ran dungeons with my brother, a resto druid, in Cataclysm, if I started off by popping Bone Shield and got a decent Blood Shield up, and gamed well with Rune Strike and Vampiric Blood, I'd have no issues with taking too much damage if I Blood Boiled every other refresh of my frosts/unholies. That was purely because of his knowledge of how to heal me efficiently.
In LFR, though, it didn't matter nearly as much how well he could heal me because he was only 33% (or 17% depending on boss mechanics) of the healing force. I had to put my effort into keeping my survivability as high as possible because I couldn't count on two other healers being able to predict and make up for if/when I didn't Death Strike.
TL;DR, I'm not 90 yet and don't know how MoP raids work, but if bosses today bear ANY resemblance to Cata bosses, you'll probably see most other tanks out-DPSing Blood DKs without having to sacrifice survivability, especially with the big debuff to our Heart Strike.
EDIT: PLUS with the change to our GCD (down from 1.5 to 1.0 sec), we're all going to have to adjust to how to land Death Strikes at the right time, making survivability take much more focus... Could be easier, could be harder. We'll see how that works out.