Most teams who make swerve drives have trouble not letting it consume their resources for the whole build season and their weight for the whole robot. For that reason, adding shifting would ruin their chances for success. One exception to the rule is team 1717. In 2012 they ran a custom 2 speed dog shifting swerve (and maybe in 2013 i'm not sure). I'm not sure what they used it for but my guess would be crossing the barrier and climbing the bridge.
Also, adding the cost of 4 ball shifters or super shifters to the cost of a swerve would most likely but the robot over budget. It does make for a cool drive train though.
