Blocking goes bye-bye
The first thing I'm going to discuss is technically not directly related to death knights, but I think it's a long time coming and it needs to come. Block needs to either leave the game or somehow be changed in a major way. This has been an issue since the day that druids first become semi-viable endgame tanks, to the point I was honestly staggered that they put in another non-blocking tank class. Considering that it looks very likely monks are going to be yet a third non-blocking tank class, warriors and paladins need to loosen the choke hold.
We already know Blizzard is planning to redesign tanking for patch 5.0, and blocking really is the elephant in the room. There are various reasons that blocking is the superior form of tanking damage, but the major reason -- the one that keeps popping up year after year -- is that it's powerful enough to allow tanks who have it to reach the avoidance cap. The magical number of 102.4% avoidance, a combined total of blocking, parrying, and dodging, will essentially prevent a tank from taking any hit they cannot parry, dodge, or block. That is, of course, the basic layman's definition of the issue, but it gets the point across well enough for our purposes.
Generally, in the last couple tiers of an expansion, it is possible to hit that cap, but only if you're a blocker class. If you only have two avoidance stats like death knights and druids (and like presumably monks will have), you're in trouble. Blizzard has said it plans to revamp tanking to be more active, to require more work to keep yourself up. If it does this, the avoidance cap just has to go. Sure, abilities like Blood Shield and Savage Defense are supposed to pick up the slack, but those really have not quite worked. At this point, I expect that block will go. It has to, to make sure all five tank classes work from an even playing field.
With block gone or the block tank's ability to cap avoidance removed some other way -- I've heard the idea of removing dodge from block tanks (which I rather like) from some quarters -- the dev team should hopefully be free to tweak balance a bit more so that non-block tanks like death knights don't find themselves inexorably losing ground at the end of an expansion. Is it the only change that needs to happen to make that a reality? Probably not, but it's been the most obviously needed fix, and one that will boost death knights and, even if it nerfs warriors and paladins, may eventually allow for more flexible balance decisions for all five classes.
Two-handed frost joins frost tanking in the trash heap
I don't like making this prediction. I like two-handed frost's playing style. It's fast and furious and requires some whack-a-mole gameplay that can be surprisingly fun without being out of control, even more so than dual wield frost. That said, Blizzard's been trying and failing to balance it all expansion. Might of the Frozen Wastes has ridden a buff and nerf roller coaster, and currently, it's pretty much fallen off. Two-handed frost is at the bottom of the barrel, and there's no current indication Blizzard cares to scrape it off until at least patch 5.0.
This is why, much like we lost all types of tanking but blood at the beginning of this expansion, the beginning of the next will see us losing access to two-handed weapons as frost. Blizzard does make this type of flexibility experiments, but it almost always reverts to one weapon type per tree. Warriors have two-handed for arms and dual wielding for fury. Enhancement shaman get to dual wield and dual wield only, even if they once wielded Sulfuras to the dismay of Alliance PVPers everywhere.
I believe we'll see the same thing with death knights. If you want to tank, you pick up a two-handed sword. If you want to dual wield tank, you're out of luck. Taking this philosophy to the DPS tree is the next step. If you want to dual wield DPS, you go to the frost tree. In both cases, Blizzard has actively quashed any attempts at dual wield tanking or dual wield unholy DPS for many patches. Frost is the next victim of this philosophy. If you want to do two-handed frost, you will be bottom of the barrel. Might of the Frozen Wastes will be gone, and there will just simply be no way to overcome dual wield's superior weapon damage.
If you want to DPS with a two-handed weapon in Pandaria, you'll need to learn to live with inferior AoE, pet management, and a rune rotation that's different from the other two trees in some pretty basic ways. ... unless, of course, my third prediction comes true.
An extensive revamp for unholy
Unholy has been on a huge roller coaster for quite some time. It started when Scourge Strike was changed from a frost and unholy rune spender to unholy only, and a completely new strike, Festering Strike, was created just to allow that to work. The ghoul pet has been buffed, then nerfed, then buffed again, and Scourge Strike and Death Coil have seen similar nerfs. Runic Empowerment was found to clash with unholy so badly that Runic Corruption was created and proved effective enough that probably everyone and his mother will take it in Mists of Pandaria if it remains in the talent tree.
Still, unholy has lagged behind frost in damage and popularity for much of Cataclysm, ever since the infamous patch 4.0.6 hot fixes. There are a variety of reasons for this. There's the trouble of dealing with a pet. There's a rune spending rotation that goes against the other two trees. There's the lack of weapon scaling due to so much damage being wrapped up in Death Coil and the ghoul. There's the lack of burst damage due to the long ramp-up time for said ghoul's damage and power moves. There's the lack of decent AoE damage, certainly nothing close to Howling Blast.
Now, two-handed unholy is currently doing pretty well, but that's primarily because the proc on the top DPS weapon of this tier stacks with unholy mastery. That isn't going to carry over into Mists of Pandaria, so something else obviously needs to be done.
I think the first step is to put Scourge Strike back on a 1 frost, 1 unholy rune cost. You'd then either make Festering Strike a blood rune strike, or bring back Blood Strike. This would put unholy back in sync with the other trees, making it easier for an inexperienced or new death knight to slip into unholy from another tree -- something that might be extra needed if Blizzard removes all support for two-handed DPS from the frost tree. This doesn't solve the DPS problems, per se, but it does the make the tree more intuitive and easier for new players to grasp, something Blizzard really should do to attract new players.
Fixing the actual rest of the tree is going to be a taller order. At the least, I suspect we'll see Dark Transformation get unlinked from Shadow Infusion in order to give unholy death knights another burst button to push, or we may see Shadow Infusion take fewer stacks to cap out.
Blizzard will also need to find some new solution for AoE damage. In theory, the AoE abilities in the top tier of the new talent trees might fix that, but seeing as the devs will need to balance those abilities around the fact that frost DPSers will take them and pair them with Howling Blast, they'll probably need to give something else to unholy death knights to bridge the gap. I doubt we'll get the original AoE Unholy Blight back, but a boy can dream.
Regardless, if any tree gets changed extensively in patch 5.0, expect it to be unholy. The disease and pet-centric game play will remain at the core, but everything around has to changed if it's going to be competitive without relying on gimmicks (no matter how fun they are) like the Gurthalak proc.
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