I don't think it should be that drastic. I guess you can say MWP has a violent past from his night in the Palace 8 years ago, but I don't think it's really that relevant here. Going into the stands is a different beast than something on the court.
Bynum got like what, 5 games for darn near breaking JJ Barea (who is about 1/3 of his size) in half last year. There's no precedent for a lengthy suspension like that. I'd say 3-5 games which would go into the playoffs would be fair. If Stern decides to include his past I think it could get longer, I don't think they will though.