Presented without commentary:

In the spirit of Aldriana's posting the Tier preview.

Rogue Legendary Daggers: First Look - Forums - World of Warcraft

Apparently the legendary gives you wings. I think I speak for us all when I say "PTR please"

pic: Glimpses | Facebook

Rogue
2P -- After triggering Tricks of the Trade, your abilities cost 20% less energy for 6 sec.
4P -- Increases the duration of Shadow Dance by 2 sec, Adrenaline Rush by 3 sec, and Vendetta by 9 sec.

I feel like these crappy bonuses (Compared to other classes) is our tradeoff for the legendary.

Thought this might interest some peers:
source for the ES forums.

Editing this since it's not a blue post, just datamined information from the 4.3 PTR.

Full (as of now unformatted) post in the 4.3 Changes Discussion thread.

You've lost much of the formatting. Looks like the poisoned modifier on Mutilate is gone (it was buffed to compensate) and the baseline of Ambush and Backstab came down. Everything else is just stylistic tooltip changes.

It may be to balance out the new legendaries for PvP (or PvE) purposes. I wouldn't be surprised.

Lets move the discussion of ability balance to the 4.3 changes thread. Thanks.

Also potentially of note: the raid AP buff (Blessing of Might or equivalent) has been increased to 20%.

I cut the RP out 4.3 Patch Preview—Fangs of the Father - World of Warcraft if you want to read that as well, below they clarify afew points about the upcoming legendary.

Rogues who succeed will receive a paired set of daggers that will become increasingly lethal as their bearer progresses along the legendary quest.

At the height of their strength, they will be imbued with the vile essence of the Old Gods, as well as the maddened fury of the Black Dragonflight—bestowing great power upon their bearer. These powers include a stacking increase to Agility which builds until dark wings unfurl from the rogue’s back, removing the combo point cost and increasing damage of finishing moves for a short time.

In addition, the wings which can be spread on command (with no combat benefit) to slow a rapid descent, allowing the rogue to slowly fall to the ground… or enact a little death from above! When it comes to dealing death, the Fangs of the Father promise legendary killing power to rogues of any specialization.

Not quite a Blue Post but from the Q&A going on right now -

Comment From Aurora
I see two new poisons given to rogues in the new talent system, does this indicate we'll be seeing poisons reworked for MoP? As it is the Assassination spec relies so heavily on the instant/deadly combo for damage it's not viable to use anything else.

5:29

Ghostcrawler: We are reworking poisons. For starters, rogue damage is balanced around the expectation of two damage poisons, which makes it really brutal to use a utility poision instead. In MoP, you will have one damage poison and one utility poison so you can choose which utility poison to use (and not IF you want a utility poison). We also want to reduce the amount of ramping that rogue DPS requires, such as removing the need for Deadly Poison to stack. (And likewise we want to make Bandit's Guile less punitive when swapping targets.)