First, in my previous post I said that Endless Winter was the PVP talent. While this still holds true, I forgot that in taking it, you usually also take Toughness, Icy Reach and Lichborne, all great PVP talents. Losing out Endless Winter hurts. Losing all of them hurts practically too much.
I've boiled down my options a bit. Focusing on which specs can double for two purposes, I've gotten six possibilities.
Just a word of warning: I've had the 3.3 changes in mind while writing this. The Glyph of Icy Touch will in 3.3 buff Frost Fever by 20%. Scourge Strike will hit harder, meaning Reaping and Epidemic will provide more dps increase.
Option 1: Blood tank/PVP
Combining the PVP and tanking talents for blood, I get something like 51/17/3. Compared to a true tank, I lose Will of the Necropolis and only get three points in Anticipation. Further, I have only 3 points to put in Subversion, Death Rune Mastery and Sudden Doom combined. Both Sudden Doom and Subversion get better with Death Rune Mastery, as it provides two extra Heart Strikes during a 20 sec rotation at the expense of a Death Strike. However, since you both in PVP and tanking regulary take damage, perhaps the loss of a bit dps is offset by the gain of a bit more healing?
Generally, I think this build loses out too much mitigation for tanking and too much dps for PVP.
The other spec would 0/51/20 Frost DW or 17/5/54 Unholy dps.
Option 2: Blood PVP/dps
51/17/3 provides the essential Blood dps talents, and adds 17 in Frost for Endless Winter and 3 in Unholy for Virulence. Actually a fairly balanced build. The two points in Improved Blood Presence could be put anywhere else as well, for example Rune Tap and Scent of Blood (for PVP, mind you).
The loss of Epidemic hurts, though. I've played with the thought of only putting 11 points in Frost and the rest in Unholy, losing Endless Winter. However, that's going to hurt in PVP.
The other spec would be Frost or Unholy tank. Linking to the awesome site Pwnwear.com. Gravity has a much better grip on pure tanking specs than me.
Option 3: Frost tank/PVP
9/55/7 succeeds in getting all essential tanking and PVP talents for frost, as far as I can see. Looks like an interesting option. Alternatively, 9/57/5 switches out the Glyph of Frost Strike with Glyph of Howling Blast, for a single-disease rotation. It drops Epidemic. I put the two spare points in Chill of the Grave, but an interesting option is to put those two points and a single point from Scent of Blood into Acclimation, but then you risk getting seriously Runic Power starved regulary.
The other spec would be 51/0/20 Blood or 17/5/54 Unholy dps.
Option 4: Frost PVP/dps
A suggestion here is 0/51/20 Frost PVP/dps, which includes On a Pale Horse. I don't have the weapons nor the talents points to spare to get DW dps.
The secondary spec would be Blood or Unholy tank.
Option 5: Unholy tank/PVP
It might work with an Unholy tank/PVP build. However, the main problem is that you lose Wandering Plague, only get three points in Blade Barrier, and lack Ravenous Dead, meaning your pet is a heck of a lot easier to kill, and only usable for keeping other players in combat. It's not a combination I would recommend.
The secondary spec would be 51/0/20 Blood or 0/51/20 Frost DW dps.
Option 6: Unholy PVP/dps
I like Unholy for PVP. I'd say something like 0/17/54 is the way to go. It'll serve moderately well as a dps spec as well. Includes On a Pale Horse.
The secondary spec would be Blood or Frost tank.
Playing what I like
All of the above are options that might to a lesser or greater extent work. However, that's only one part of the question what to do. The second is what I like to play.
Listing what I like about the various specs in various roles.
Blood is awesome for the self-healing, particularily in PVP. I'm not sure I like it as a dps spec all that much. For tanking, I like the skill cap resulting in being able to use Death Strike at the correct time. For max threat you will need to spam it. However, for survival, it can be handy to wait some seconds with Death Strike until you take damage. I've had success doing this with boss abilities that are announced in advance, such as Meteor Fist on Koralon and the big AoE on Emalon.
What I don't like with Blood is that it isn't so good for AoE, but then again I'm comparing to Unholy which rocks the AoE hard. In PVP it's also much more physical damage compared to the other two, meaning I don't tear through pallies and warriors as easily.
Frost is great for tanking because of the extra mitigation. It's also great to have Icebound Fortitude lasting 16 seconds, particulary in PVP where it means 16 sec of stun immunity. I like Howling Blast because of it's snappy aggro. What I don't like about Frost is that I need to watch for procs all the time and align them correctly for max dps. Fortunately this is less of an issue for a tank, and for PVP you can't afford to wait with procs, you blow when you get the chance. However, I'd like to try DW tanking in 3.3, and only Forst can offer that without a serious threat loss. I don't think Unholy can put out enough threat while dual-wield tanking. If I do that, I need to go with option 2 or option 6, combining PVP and dps with my other spec.
Unholy is great for having a permanent pet, great AoE, powerful dots and great debuff. In addition, I find the rotation fits me fine, much more than Blood and Frost. It feels like they're slightly less tough as tanks against physical damage, but way better against magical damage. I think Desecration is a kind of bad snare. It takes so long to kick in that the target has time to get out of the area, provided they're moving in a straight line. Without Chains of Ice to fall back on, I'd have given up Unholy for PVP a long time ago. For PVP it's also great that Ebon Plague counts as an extra disease for removing diseases.
Conclusions... sort of
Of the six main options below, I find option 5 to be the worst. Option 1 and 3 combines tanking and PVP, but at the expense of dps. I might end up sacrificing so much dps that I have trouble bringing my enemies down, and that's going to hurt.
I want to test out what I like about a single-disease Howling Blast glyph Frost build somtime, option 3. Perhaps I like it, perhaps I don't.
For the moment, I'm using Option 6, Unholy PVP/dps and Blood tank. It works out well, but I'd like to try the other options as well. If I don't find any I like, I'll return to Unholy PVP/dps. It rocks.
I also think that tanking and PVP are the two most important aspects of the game for me. If I deal 500 or even 1000 dps less (as long as I'm above 3k) it does suck a bit. Howevever, if I take 10% more damage as a tank, it's downright devestating. Similarily, if I can't stick to the enemy (in effect, get snared all the time), I'm going to end up so annoyed I might just skip out of PVP alltogether. That means I'm much more inclined to go with option 2 or 4, since they don't sacrifice anything from the tanking spec, and effectively go dps with a pure PVP spec.
I'm going to pay a lot in respeccing and reglyphing in the following weeks.