"That's not to say that it hasn't ended up inferior to Affliction/Destruction in most situations; it has. But not underpowered." Link to source.
As Warlocks have three specs to choose from, and one is said to be inferior in most situations it doesn't really matter what that third's power level is relative to the other 20 DPS specs on other classes in the game because they aren't what it's in competition with - it's in competition with Affliction and Destruction. Players are told and encouraged to pick the spec that will perform better in most situations by other players, by the community and by their own desire to be the best; "Which is the best spec" is probably the first question anyone asks when picking a new class. That tweet linked above will be on the front of this, and other websites in the next few days and it the only words that matter in it are
inferior to Affliction/Destruction; resounding confirmation from a developer of the spec's position.
Anyone who had any doubts about the spec just had them confirmed, whether it's players who wondered if they might be underperforming, or their raid leaders who thought they might do better with another spec; they're going to switch. Hardly anyone is going to come into the spec afresh. If there's no intention to act on it, then it was a really, really stupid thing to say with so long of the expansion left.
Venting aside, going into WoD though, what are the shortfalls that need fixing? Target switching? Sustained AoE? Multidotting? Cleave? How to fix?