World of Warcraft players, come in!

Not exactly helping the enemy. If you recall the interview, we're helping a "Pure" Black dragon prince who isn't under Deathwing's control, nor is corrupted by the old gods.
He's got his own "Agenda" to attend to and is looking for the rogues to help him as they deal with the similar "Shady Business" he's dealing with.

 Spoiler

So players who play through the Cataclysm quests in the Badlands will remember a questline around this uncorrupted black dragon egg. It was free of the taint of the Old Gods. So what is going to happen is that black dragon egg eventually hatches and there is a black dragon prince who is pure – he’s not a minion of Deathwing; he’s not corrupted by the Old Gods. But that doesn’t mean he is necessarily a good guy. He’s kind of out for himself, he’s kind of got his own agenda, and to bring his plans to fruition he contacts the Rogue because Rogues are a little shady, always working in the shadows, always playing a number of games and has other things going on. The black dragon prince reaches out to the Rogue character and says “If you help me out, I’ll reward you with these increasingly more powerful daggers”.

Asides from that, Blizzard wants to give Rogues another "Dual Legendary" similar to the Warglaives back in BT. One "Mainhand" dagger and one "Offhand" dagger, which will EASILY be BiS for all 3 specs. Plus Sinister Strike will be able to be used with these daggers equipped, thus the rebirth of "Combat Daggers".