GM has 2 RWD platforms, Sigma and Zeta.
Sigma stays with Caddies, no "ZETA CTS" ever.
Zeta is to be used with the new Camaro, and others, but it is still 'unofficial'
Also, it is a myth that the Holden Monaro/GTO is a "Catera". It is actually a stretched Opel Omega, once called "Opel Senator". Holden took it after Opel decided to not make more Senators.