Battery-swapping qualifies for the ZEV credits because it allows a type of rapid "refueling" of an electric vehicle, similar to filling up a tank with H2 for a hydrogen fuel-cell vehicle. Forward-thinking automakers can sell these credits to automakers who need them, generating revenue. Such sales helped Tesla achieve its first profitable quarter during the Q1 of 2013. CARB will publish its proposed rule changes in early September, after which there will be a 45-day comment period before anything's decided.
Tesla, which first said the Model S was designed to allow battery-swapping in 2009, demonstrated them last month at the Tesla Design Studio in Southern California (we've provided the video again below). The automaker planned to build battery-swapping stations near its especially busy Supercharger fast-charging station locations and is not saying whether CARB's potential rule change will cause the company to ditch its battery-swapping plans. There are more details over on Green Car Reports.