I'm not the one to do this, but what about creating a Wiki spreadsheet for each Supercharger station that people could post probable dates and times of planned usage? Would be nice to see in advance of a trip, that the Barstow station has planned usages during the morning, but not in the afternoon on a given date. This wouldn't be a reservation system so much as information. Perhaps could include email/cell phone info for those making entries. So I'm driving down I-5, I can call someone who is planning on a 11 AM charge at Harris Ranch to see how it's going.
But like I said, I'm not the one to do this. And TimDorr lives in Atlanta so not sure he'd be interested in tracking Superchargers in CA. Any volunteers?