So first of all, I understand that not all changes are in yet I am more interested in what the role of a DK will be in the WoD meta game in PvP. I think a lot of the discussion in the changes thread about Necro is more from a PvE stand point and some people don't understand what necro means to a DK. I guess first of all I should point out the very few reasons DKs are brought into rated play right now:
RBG:
Dks are brought in for massive spread pressure, death grip, and pre-stacking necro on kill targets. As I understand it so far, we will still do a lot of damage and still retain death grip so it might not be a huge loss here. In RBG settings it is actually somewhat hard to get a proper stack on a kill target simply because of all the "smart" aoe healing being thrown around. I can say though, that many a game I have played has been won because we got a good kill on a target that was wounded but with a giant necro stack that could not be recovered from once we switched to them.
2v2:
Necro is currently huge here and pretty much the only way a DK can land a kill. It is unlikely that you can run double dps as a DK to any high rating, mostly because of the DK defensive toolkit being so slim. So in order to land a kill mostly solo as a DK you have to have to use necro wisely. The difference between a good DK and a beast is when they choose to stack up a big necro. Frost suffers from being able to do huge amounts of spike damage, but not quite enough to finish a target before they run out of runes, so most 2v2 play is unholy. Unholy is built around constant pressure and in order to land kills they need necro to protect soul reaper and to a larger effect make all those small ticks of pet, dot, strike damage amount to something scary to heal when behind a healing absorb. Without necro all those small hits are easily swatted away and unholy would need some serious big guns which would put them into season 5 mode with the garg, pet, diseases and then hard hitting strikes as well.
3v3:
It is much the same as 2v2 except your main job is to facilitate kills for your dps partner. Necro is how you do that right now because of the necro mechanic absorb not being affected by defensive CDs. You and your hunter/war partner start in on a target and when they pop defensives that is when you keep pressure on them with necro while your partner locks down the heals. Then when their defenses are down they have a giant stack, your partner starts back and the target most of the time dies.
The problem I think with the current discussion is that lots of people seem to think that necro is just damage in a different form. So why not just replace it with regular damage? Necro does not work that way, and people that use necro as just regular "delayed" damage are basically using it wrong. Necro has a couple of main uses:
1.) Delayed damage that is not readily apparent. This is in the case of large skirmishes where the healer will not see a target as being in trouble until they have a large deficit to make up.
2.) Keeping pressure up through defensive cooldowns. This is the real big benefit of necro, something that normal damage just cannot do.
3.) Covering DK execute mechanics. Soul reaper sucks pretty bad. We have to have necro stacks to keep people in that range long enough for soul reaper to proc. Even then it does not mean a kill, just more pressure.
4.) Assisting partners by artificially keeping a target in execute range. With the way healing works if necro were just straight damage then targets would get healed out of execute range pretty quickly which reduces your damage and your partners (in most cases).
Now the interesting thing that I would like to discuss is where will DKs fit into the WoD meta? If it is true that healing will be less whack a mole from 20% to full and more triage healing, then I understand how necro would be too strong. I don't think they will ever get healing into that state though because they have said time and time again they want to do this and all we get is more burst. Without necro what does a DK bring? death grip? damage? Why bring one of the squishiest classes if all they can do is damage? We have no CC, we are the least mobile melee by a long shot, when focused it not only tanks our damage but we just fold over and die... so what is the point of bringing a DK if they don't have the one thing that they were brought for anymore?