My primary concern is going to mostly be blood vs unholy, since frost is essentially for tanking. My biggest concern is how valuable the 0.5s gcd is going to be vs 15% damage caused via blood presence, which is just absolutely huge.
Your auto attack DPS will be the same, (15% extra haste = 15% extra damage), so the real question lies in the 15% damage via your specials vs the ability to pump out those specials quicker. It's too early to tell right now just how valuable that faster gcd will be, but I can definitely see the benefits. Sure, your first plague strike might do 15% more damage in blood presence, but your second one is going to take 50% longer to hit (1.5s gcd vs 1.0s) the target. In addition, it can be pretty game-breaking to be caught mid-gcd and unable to interrupt that game-winning heal because you were in blood presence instead of unholy. Time will tell, but obviously not many people will be using unholy presence just yet, as pvp is all but dead right now on the alpha servers. There's just no point to using unholy aura right now, so it isn't going to get the testing and feedback it needs just yet.
As someone who held a 3v3 team on BG9 with some notable players with a 2300+ rating in season 2, and had several other teams that were 2200+ in 2v2 and 5v5, I take this area very seriously.
First and foremost, let's talk about mobility:
Unholy aura seems like a fantastic talent, but it's position in the tree makes it mutually exclusive to several other builds/trees. 10% Extra run speed for the group that will stack with your run speed enchant seems almost required, especially in a tree that has such amazing pvp talents such as bone armor, anti magic zone, unholy command (yes, 10s lower cooldown on death's grip is huge), on a pale horse, and lichborne. The initial problem with ret paladins was their issue of getting kited all over the place. This was solved in part due to the pursuit of justice talent relatively early in ret (even though I think more paladins than ret could really use this talent in pvp, especially holy). This talent would also be an assassination rogues' best friend, granting them a total of 25% movement speed increase.
Next we have chillblains, which seems required for one basic reason: Chains of ice has way too many drawbacks. Deathknights have 0 dispel protection for their frost abilities right now, and with chains of ice being so ridiculously expensive to use, in addition to its 20s cooldown (why?), I just don't see any frost build being successful in pvp without chillblains. This is essentially the frost tree's version of unholy aura, except it isn't really active 100% of the time. Once you factor in how ridiculously easy a lot of classes will be able to cleanse it, not to mention you can't exactly trinket out of getting chased by someone faster than you (as you would be faster than most with unholy aura), this talent becomes less attractive for your hardcore pvper, and even less so for your pver.
Death's grip will act as a wonderful "get back over here" type of ability, once our target makes his/her escape.. but as of right now, it's a little lackluster, as the target that was kiting me right before using it can typically run right back away, especially if I'm still snared. I wish this ability had a 1-2s root tacked onto it as well. There seems to be some lag when Using it. when I use it on pvp players, it takes them a few seconds to get pulled back to me as they fly through the air, and sometimes they land next to me out of melee range. Without unholy aura, using this ability in its current form does me absolutely zero good sometimes.
Speaking of death's grip, I would rather have this ability use 10 runic power instead of an unholy rune. I mean it's an ability that's essentially used in a situation like intercept, where you need to get back on your target, yes? So you more than likely already have a bunch of runic power to spend, and nothing really good to spend it on. I think DG would be an excellent ability to have use RP. Right now, all I really use it for is deathcoil spam, and I find myself wishing I had more interesting abilities to use it on. Not to mention, this would save an unholy rune and allow me to use my bone armor/anti magic shell/diseases more often. Wouldn't it make sense to use an unholy rune to eat that incoming spell via anti magic shell, which would charge your runic power, and use that RP to pull the caster towards you? Seems more logical to me to do it that way, rather than to spend an unholy rune eating that spell, and another to pull the caster towards you, and then use all that runic power on..... a deathcoil? And then not have any unholy runes available to bone armor/disease.. Please consider this change.
Chains of ice I won't really touch on that much, as I feel this ability has too many restrictions placed on it. Double rune cost, 20 second cooldown, and absolutely 0 dispel protection make this ability a lot weaker in practice than it looks on paper. Even if it only cost 1 frost rune, and had 0 cooldown, I could still see a lot of classes simply trinketing out, or dispelling it off of themselves or their teammates. Is it really so OP to have so many restrictions? If anything, I think this is another one of those abilities that would probably be better off using a discreet amount of runic power, rather than runes.
3) Runic Power PvP Utility:
I can't stress this enough. Death knights have essentially ZERO utility via runic power for pvp builds right now, other than deathcoil spam and the occasional icebound fortitude. Ok, so as an anti caster, I have one single ability (which is essentially pummel), that uses runic power. That's it. I feel like our control/utility type abilities of chains of ice and death's grip would be much better off if they used discreet amounts of runic power. It feels incredibly boring to only really have deathcoil and the occasional mind freeze as your only option to use runic power on vs casters.
Use the 51 point talents you say? I could see possibly hungering cold be useful in pvp, but definitely not unholy blight. Dancing rune blade would be fun to use, if it weren't for the fact that deep blood builds (51+) have access to neither chillblains, nor unholy aura. Deep blood spec DKs will be the most easily kited melee class/spec in the game.
Even still, those 51 pointers are on lengthy cooldowns. Where is the utility between? I'm beginning to feel like that, vs casters, my runic power bar is essentially my deathcoil charging bar. At least vs melee, I have the option to use icebound fortitude every minute (which is still rather lengthy, considering the lack of variety of RP abilities).