Why not make it so that SoaB adds one extra side to every die rolled per level? This would simultaneously make it less useful on chain weapons, while making it useful at all for rocket launchers, shotguns, etc! (Pistols would be equally effected) Thus, SoaB becomes less game-breaking, but simultaneously is useful for all weapon paths meaning that the whole chain weapon dilemma is neatly sidestepped. I also think this would be a good idea for the flavor of the game. A true Son of a Bitch wouldn't find himself confined to a certain weapon type; he'd be kicking ass and taking names no matter what weapon path he was using. It would also make SoaB truly the inverse of TaN- a generally useful skill that can be used to fill in the gaps of any skill set.
Opinions?