The Q&A finally looks like the developers are stumbling across the problem with rogues:

"This next bit might start a firestorm of controversy, but we heard from a lot of 10-player raiders who asked "Why make a rogue legendary? We don't have a rogue." When we asked why, they said 'Rogues don't bring anything we need, so we don't want them." That's not cool. I'm not saying the legendary is the answer for why bring rogues, but you should feel like you have room for rogues without sacrificing something else and that rogues should bring something that makes you happy they are there."

And that is indeed it in a nutshell. Rogues literally do not bring anything the raid particularly needs. We haven't brought top dps for more than a year and are regularly beaten by a huge number of specs in anything but trick fights when blade flurry can pad the numbers. We have no serious utility to compete with druids, warriors or DKs. We can't get to off-heals or off-tank like druids, priests, warriors, DKs, shamans and paladins. We have all of the liabilities of melee unlike boomkins, elemental shamans, shadow priests, warlocks, hunters and mages with none of the plate toughness of the other melee. There really isn't a reason why a raid leader should be even as happy with a rogue compared to another class, much less particularly happy that the rogue is there.

The developers have really boxed themselves into a corner over this. See this Q&A:

"We are very interested in opening opportunities for more hybrid gameplay in druids, as you can see in the level 90 talent tier, while still allowing an option for players who want to never do anything outside their role. We don't intend for that added hybridization to be offset by any sort of DPS nerf. While DPSing, a druid's DPS will be entirely competitive with other DPS. We hope to see druids that do things like, "DPS in Cat Form most of the fight, but during one phase, when healing is super difficult, pop out of Cat, hit Heart of the Wild, Tranquility, and spam heals on the raid to help top everyone off, then go back to Cat and resume DPSing." In that sort of the situation, the Cat will have spent less time DPSing than other DPSers, but his/her DPS while DPSing would have been competitive, and in exchange helped save the raid when healers were falling behind. You can probably think of many situations where this would be useful in raid content, or in some 5man content, and frequently in PvP. To clarify a bit further on how the druids will perform at their off-roles: Ferals and Guardians will have Nurturing Instinct, which increases spell power based on Agility, and Balance and Restoration will have Killer Instinct, which increases attack power based on Intellect. They will have a smaller toolbox of spells for their off-role, but the strength of those spells will be competitive, when under the effects of those hybrid talents."

This is exactly why any raid leader in their right mind would take a good druid over an equally good (or maybe even better at playing his class) rogue. They intend for the hybrids to do equal dps, as well as bring much more to the raid when the raid needs it. And it sounds like they intend to make this problem worse, not better.

They are going to have to come up with something brilliant to avoid this, and considering they apparently didn't even realize it was a problem until the legendary for rogues was announced, I'm very worried. Especially with monks making the problem even worse.

The MoP Talent calculators are updated.
Talent calc updated! - Forums - World of Warcraft
Talent Calculator - Game Guide - World of Warcraft

Daxxarri did a bit of rogue posting here - Shiv Changes - Forums - World of Warcraft

Q. Will the thrown weapon talents have a chance to apply one or both active poisons?
We're not sure about this yet. It's more likely that we'll apply damage poisons than the non-lethal ones, especially in the case of Shuriken, because a fairly spammable ranged snare is probably too good.

Sorry, guys. You can still use Shuriken + Deadly Throw though!

Q. If I have Deadly Brew, will Shiv amplify that Crippling Poison effect in addition to my active poisons?
No. Deadly Brew isn't the same as having Crippling actually active.

Q. For clarification, how exactly do active poisons work? One lethal, one utility, both with potential to proc from both weapons?
One Lethal, one Non-Lethal, and both poisons are effectively on both weapons. Whenever you land either a mainhand or off-hand strike, you have a chance to apply both your Lethal and Non-Lethal poison.

Q. How does poison proccing work now, and what does that mean for weapon speed.
Poison procs are largely unchanged, except, y’know, for all poisons being percentage-based in the future. We’re looking to get rid of the "fast 1.4 speed dagger" thing. The plan is for offhand daggers to just be daggers and interchangeable with main hand daggers. So we're anticipating Assassination and Subtlety rogues will use 1.8/1.8 daggers for the most part, while Combat will use a 2.6 main hand and a 1.8 offhand dagger. I know some of you noticed a Main Gauche change, and the intention isn’t a nerf. If it needs adjustment, it’s important to remember that numbers are still in flux.

On a separate note, while we don’t have an elegant system in place for it, we do know that a lot of Combat rogues want to at least have the appearance of dual wielding swords/axes/maces. There are a lot of hurdles, but maybe we’ll find a good way to deliver on that. No promises though! So, again, don’t get your hopes up too high.

Q. So, how about an offensive dispel using the shiv system (perhaps as an alternative to Mind Numbing)?
It's something we might consider, but if too many people have access to an effect like that, then magic buffs are increasingly devalued, and that causes all kinds of problems. For example, something like Hand of Protection is cool, but significantly less meaningful if too many classes out there can remove it with a button press. So, we'll think about it, but don't get your hopes up.

Q. Is Mind Numbing nerfed, now that it won’t affect all casts for the duration?
That's a bit of a misunderstanding. Base Mind-Numbing is unchanged and works as it does now. The new Shiv effect stacks on top of the base Mind-Numbing, and is more than triply effective on the single next spellcast.

Q. Any chance of a sweet UI element warning the rogue that he’s approaching 5 stacks of paralytic poison, or letting him know that it went off?
Making it easier to track buffs and debuffs in the UI, including using the Spell Alert system, is something we're always looking at.

Q. Y U NERF CRIPPLING?
Sadly, because it was too good -- which is pretty much the same reason anything ever gets nerfed. Basically, we're looking to chill out some of the passive, automatically-applied snares on some classes get because there's no real gameplay to them beyond just I touch you and you're snared.

Crippling is an important tool though, and we didn't want to take it away entirely. By lowering the base snare and allowing Shiv to still apply the -70% form, snaring opponents or kiting other melee classes that also have snares becomes something you'll need to think about and manage.

Is Crippling going to last 12 seconds in PVP now, instead of 8 seconds?
Nay. PvP durations are capped at 8 (and nothing should break that rule), but PvP durations aren’t shown in the tooltips.

Q. Under the proposed system, it looks like it won’t be possible to take both Paralytic and Leeching Poison. Will we have to have to choose between Paralytic and Crippling?
You can take both Paralytic and Leeching, but you'll be able to actively make use of one at a time. That said, switching poisons isn't necessarily impossible in the heat of combat -- the cast time on swapping will be fairly short.

That said, we're taking a look at the decision involved in the current placement of the different Poison-related talents, and that's something we may reevaluate. Still early days yet – and that applies to everything in this list.

Q. But Daxx! RAWR RAIDING! What's this PvP nonsense?
We'd like Shiv to be useful when raiding too, and increasing the availability of such effects makes it easier to design encounters that permit them to shine. It bears mentioning that, even now, the various Shiv effects could be useful in existing raid encounters. There’s no reason to expect that they couldn't be useful in Mists raid design too.

Also, there's more to PvE than raiding. Just because a talent isn't useful when you're fighting Ultraxion doesn't mean it isn't useful in PvE at large. There's still leveling (remember, tier 1 talents should ideally be relevant and useful to a level 15 player!), outdoor dailies, the upcoming challenge modes, and more to consider.

Sooooo… Does this mean that rogue damage might go up if we lose some control/mobility/survivability?
We want rogue PvE damage to remain top-tier. But yes, if rogues end up with less control or mobility or survivability, and they have to choose among those areas, then that allows us to safely improve their damage potential in PvP while keeping the class balanced overall.