Reasons for the sequel platform's demise are allegedly that the first hydra-formed Kappa is just too expensive to fabricate; the cars based on it use expensive, hydra-formed parts; assembly requires inordinate amounts of human labor; and GM didn't make its money back fast enough to justify the investment in a new RWD – read: thirstier – platform.
The current Kappa's suspension and design geometry aren't shared with any other car;, the platform was created to accept one engine, the Ecotec 4-cylinder; and it served under only four varieties of the same car: the Pontiac Solstice, Saturn Sky, Daewoo G2X and Opel GT. It was a lot to ask such a limited platform to achieve the volume's GM needed with cars on expensive underpinnings that didn't demand expensive prices. And if the rumors are true, then your Solstice GXP could be worth more than you expected, and sooner than you expected.
[Source: GM Inside News]