This is a case of CalTrain listening to its riders--and rider/bloggers! (I first mentioned the idea here (and I emailed them too) back in 2009). Props especially to Murph who went to JPB meetings and got them to pay attention and actually do it.
A weekend trip from RWC to 4th & King will take 35 mins on a bullet instead of 55 mins on a local. For outings with kids, I think that pushes us into "Dad's taking us on the train" territory, vs "Dad's making us ride the train"... Should be fun.
It's officially just an experiment. Hopefully it'll run long enough so that we get some warm weather, where recreational ridership should really take off.