While I have no problem from that, obscene gestures tend to get anyone penalized in some form or another. You're subject to ejection and/or fine for showing obscene gestures or mouthing bad words on the jumbotron during a game. That's an ordinary fan.
Rinaldo should be under an even tighter microscope. The NHL is a business and its primary purpose, while to entertain fans, is surely to recruit to new fans. It's prime target demographic isn't casual fans that are old enough to not give two ***** about a middle finger. Their target demographic is young children who have the highest potential of reaching the highest hockey fan avidity out of any fans. The higher the avidity of a fan, the more revenues the league will make (longer duration of being a fan, more willing to buy apparel of team, more willing to go to the games than watch on tv, more willing to watch hockey on tv than another program... etc.).
The problem with allowing a player to go unpunished for such an act is that parents won't want to expose their children to such behavior at such a young age. If the NHL doesn't punish him, it sets a precedent for other players to act disrespectfully towards the crowd, and that will only harm the NHL's end goal of catering to these young kids and boosting revenues now and for the future.
I'm expecting a fine. No suspension. But discipline will likely be taken, either way.