The new rule against head-hunting emphasizes a prohibition on "“lateral, back-pressure or blindside hit to an opponent where the head is targeted and/or the principal point of contact.” Under a strict reading of that language, the rule might not apply here. Mathieu Perreault and Armstrong meet, more or less, face to face (or as this screen capture from the Comcast Sports Net feed suggests, elbow to face). No "lateral, back-pressure, or blindside" occurrence in evidence there.
But actively thrusting an elbow at the head of an opponent is covered under other rules. Rule 46.1 defines elbowing as "the use of an extended elbow in a manner that may or may not cause injury."
Further, Rule 46.3 gives the referee the discretion to call a major penalty on "any player or goalkeeper who uses his elbow to foul an opponent. A major penalty must be imposed under this rule for a foul resulting in an injury to the face or head of an opponent."
Rule 46.4 allows for further penalty: "The Referee, at his discretion, may assess a match penalty if, in his judgment, the player or goalkeeper attempted to or deliberately injured his opponent by elbowing."
Whether Armstrong could be cited under rules for the maximum treatment here under Rule 46.4 is doubtful (a lot of Caps fans would say "yes," Thrasher fans would disagree). But it is a no brainer that Rule 46.1 applies, and certainly given the enthusiastic manner in which Armstrong applied his elbow to the jaw of Perreault, the referee's discretion to call a major penalty cannot be discounted... if you're really in the business of trying to stop head shots.
However, no penalty was called on the play. And, Armstrong is not a "repeat offender." Despite a reputation for sharp elbows, he has no record (at least in any search we did) of suspension by the league.
Will Armstrong miss time over this? We're betting on "no." Why? Well, it's in what Armstrong had to say about the play...
“I just banged a forecheck on him. I had a pretty good line on him. He’s a pretty good little shifty player and I think he kind of bailed out there at the end. I saw the replay. If anything I just tried to get a piece of him. I didn’t mean to get my arms up in his kitchen like that. It just happened so fast. I just tried to get a piece of him. I talked to the ref afterward and he said he ducked out of the way and fell backward (emphasis added).”
Pereault ducking out of the way is not the action to which a penalty can be applied. The issue is Armstrong and his elbow. All Perreault's actions did was to enable him to avoid what might have been serious injury as a result of that elbow. If the league decides not to give Armstrong a vacation, you can decide for yourself if the league is serious about eliminating head shots on the ice or just writing rules for the sake of appearing to do something about the problem.