Let's talk about the biggest changes first. I covered the new sub spec details pretty thoroughly a few weeks ago, but a quick recap can't hurt. In terms of PvE viability, sub is dead last, and it's not even close. None of the changes make up for the forced PvP / survivability talents that we're required to take as we make our way down the tree. While our other trees make look more similar to sub once Cataclysm is released, we are still firmly in the Lich King's grasp and the dominance of a DPS-oriented tree is too strong for sub to overcome.
Forget about it for now, and hope that a future patch or expansion brings sub PvE back from the dead. I'm not going to post a "best possible" sub PvE spec, because frankly, you can throw your points just about anywhere in the tree and you're still so far behind Mut or combat that it's not worth trying. The spec misses all of the hit, expertise, and CDs that make combat so potent, or it misses all of the poisonous goodness of a Mutilate build. Even if you had some hybrid gear set with enough hit and expertise to cover the spread, you're missing out on all the other stats that push Mutilate and combat to their current levels.
Now, all of that goes out the window if we're talking about PvP. Unfortunately, I don't know if sub is going to be as versatile as our standard Mutilate/Preparation PvP build. Shadow Dance is overpowered against certain classes (Hunters with Flares come to mind), but faces the same challenges that a combat PvP spec would face. Without Deadly Brew, you immediately lose 50% or more of your poison damage by relying on Crippling Poison, while both Backstab and Ambush have positional requirements that make them incredibly difficult to use in a fast-paced PvP environment. Waylay may be intended to replace Crippling Poison, but it simply can't do the job if we have to be behind our target to apply it.
I think a strong subtlety dagger build could be a lot of fun to play in a battleground or world PvP environment, but for serious arena play, I don't expect many rogues to spec into a Shadow Dance build unless they're facing a specific opponent. I'd be tickled pink to be proven wrong, but let's face it: we all ignored Mutilate in TBC due to its positioning requirement, why would Backstab be any different? Hemorrhage will simply not cut the butter, as it's not tied to Waylay and doesn't see the 30% extra crit that we get from Puncturing Wounds.
What? Wait... what? Three new useless glyph buffs? Your guess is as good as mine as to what Blizzard was thinking on these, but I pray they were added as a comedy item. The Feint glyph is a nice idea, but there aren't any fights that require it, and cutting DPS for survivability on a small scale is not the way a rogue handles that problem. Unless it is life-threatening or avoidable, you let your healers heal through it. They're actively working to allow themselves the capability of healing you through these AoE effects, so why would we insult them by trying to do it ourselves? Focus on your DPS: the quicker the boss goes down, the less time your healers will have to deal with that AoE damage pulse.
Rupture ticks can now crit
First, they came for the warlocks and shadow priests. Then, they came for the shamans and restoration druids. Finally, they've come for us. Rupture ticks are now able to crit, and unlike our poison crits which are based on our spell crit chance, Rupture crits based on our physical crit chance. With a Rupture-heavy build, this means that agility gems become significantly more valuable. There's only one problem: no PvE spec is particularly fond of agility.
As a general statement, for any rogue ability that scales with Attack Power and physical crit chance, agility is better than AP in equally balanced portions (10 Agility to 20 Attack Power). Unfortunately for Mutilate rogues, they're running into serious White Crit Cap issues in ICC gear, and adding more agility to their gear is simply exacerbating the problem. In addition, poisons don't scale their critical strike chance via agility, so Attack Power and Haste are more potent for boosting our poison damage. This means that Rupture is already critting as often as possible if you're running a Mutilate build, so the finisher has no room to grow with new gear.
This means that Mutilate really doesn't want to socket Agility at all, and both AP and Haste are sub-optimal gems for a Rupture build. The final nail in the coffin for using Rupture with Mutilate is the strength of Envenom: it will typically out-damage a Rupture, and so Rupture is basically out of the question. The fact is that Mutilate builds don't have the available points it would take to reach deeper into subtlety to pick up Serrated Blades, and without that, Rupture can't compete with Envenom, even if it does crit. Rupture is in the ideal situation (high AP, high crit) and yet it's still not viable.
Now, Combat actually does have the points it would take to pick up Serrated Blades. Unfortunately, as we've seen with all of our current 20/51/0 builds, the second tier of subtlety is so awful for PvE that we're essentially throwing away 5 talent points. With any given talent point providing around 1% of our overall DPS, I think it's pretty obvious that losing 5% of our overall damage just to add Rupture to our rotation won't be worth it. The question is: can Rupture with crits beat Eviscerate, even without Serrated Blades?
That's one you'll have to answer for yourself on a spreadsheet. Envenom beats Rupture so bad that Rupture's kids will get the bruises, but the Rupture vs Eviscerate battle is far closer. Unfortunately for Rupture (I feel like I've been saying this a lot today), most combat rogues have already given up their DoT ways and are gemmed / geared for ArP. Eviscerate loves ArP, Rupture literally gets no benefit from it. The old rogue adage of "Rupture always does more damage than Eviscerate" is simply not true now. The reason it used to be true was due to high enemy armor, which is no longer an issue. So again, rogues of today's game are simply not designed to start using Rupture again, and haven't been for some time.
Depending on your particular gear, and particularly for combat builds with low ArP, you can actually make a Rupture build work pretty well. Only a spreadsheet can tell you for sure, but I've been seeing a lot of solid math showing a DPS increase by going to a Rupture-heavy rotation. The basic idea is to scrap Eviscerate for Rupture by picking up Blood Spatter and filling Ruthlessness out instead of getting Improved Eviscerate, and swapping your Eviscerate glyph for a Glyph of Rupture. I've also seen some math that argues that dropping a different glyph will be a lower DPS loss, as we'll still be popping off a few Eviscerates when Slice and Dice and Rupture both have a long duration remaining.
The simple fact is that it's going to be a close call, and so I wouldn't recommend running out and regemming unless you really, really love Rupture. Rupture builds are weaker on any fight with heavy swapping (Deathwhisper, Valithria, Putricide) and stronger on our burn fights (Saurfang, Festergut, Rotface). Almost laughably, all of the fights that favor combat are also Rupture's worst case scenarios. Combat's huge boon is its quick target swapping and on-demand burst damage via cooldowns, whereas Rupture's best-use case involves a single target and steady damage over a long period of time. Adding Rupture to Mutilate's already second tier target swapping would simply be an insult to injury.
Sub PvE is still dead, sub PvP may be the most enjoyable spec in the game but won't get you gladiator. The new glyphs will probably become somewhat of a joke among the rogue community, so if you catch me telling you to glyph Deadly Throw, realize I'm only teasing. Finally, Rupture can be useful, although Envenom beats Rupture like Rupture owes Envenom money, and Eviscerate can put up a decent fight when hopped up on ArP. I get the feeling Rupture just showed up late to the party and realized that everyone had already left. Wait for an updated spreadsheet and check for yourself, but if you're combat, Rupture may very well be in your future.