When automakers are getting a new vehicle ready for production, the main specifications are generally locked down about 18-24 months before production starts. After that point, validation testing and calibration continues right up until Job One and changes are restricted unless a major problem is encountered. Because of the potential impact on other vehicle systems, any changes are necessarily limited. Meanwhile, once a current generation is locked down, the advanced engineering teams move on to further evolutions.
UK magazine AutoCar is claiming that the Chevy Volt and its European twins the Opel/Vauxhall Ampera will be one=generation vehicles. After the first generation, the publication claims, the Voltec propulsion system will just be applied to other existing vehicles like the Astra. While Voltec will almost certainly be mainstreamed just as Toyota has done with its Hybrid Synergy Drive, the Volt will apparently live on. GM spokesman David Darovitz tells ABG "there is about much truth to this as I am going to be in the next Superman movie. We're already working on Gen II." GM discussed the Gen II Volts back in March. The Ampera may be a different situation however, as GM attempts to sell off controling interest in its European operations. That variant may fade away in the coming years.