Cheap shot in my opinion. Doesn't look like Salo is even looking to throw a big hit, much less a dirty one.
This is why discipline has to come from the league. You can't just assume someone is going to throw a dirty hit, and use that assumption to justify a dirty preemptive strike. Vigilante justice never works, and only causes more injuries and injuries to innocent people.
Marchand absolutely should be suspended. If I remember correctly, he has a history of going for the knees too. 2-5 games I'd say, depending on his repeat status.
Why doesn't Marchand take a page out of Datsyuk's book and just match Salo shoulder for shoulder to gain an advantage? I've seen Dats do it a million times against bigger or smaller guys. It's a clean and effective way of gaining position on a similar play. I don't want hitting out of the game but hits like this are a joke, its contact made below the waist with an attempt to send a guy landing on his head.