I'm feeling a bit better now that Guion M posted this over at CZ28:
You nailed Zeta on Holden's side and Pontiac's plans.
Outside of that, Sigma's writing is on the wall but I wouldn't expect the next CTS to grow in size beyond the 2008 model. Zeta is a cheaper and better structure than Sigma, so it's essentially an open & shut case to move it to Cadillac.
In addition to the Camaro & Impala, I'd also expect the El Camino here during the 2009CY, making it a really fun time to be a Chevrolet enthusiast.
I haven't seriously believed Chevrolet would have a large coupe since it began looking very likely Holden would be making the Monaro replacemnt in Australia instead of in North America (last fall). The whole basis of building the large coupes here in NA was that Chevrolet's volume would make it worthwhile. While I can easily see Chevrolet importing a version as a Chevrolet "GTO" (it's going to be sold in the Middle East as a Chevy anyway), I don't see 35-45,000 G8s and another 12-15,000 GTOs and another 150-160,000 Holdens for local and world distribution leaving much room for another 15-20,000 Chevy coupes. I'll be the 1st to admit it's possible (to fill out capacity), but I wouldn't bet my beer money on it at the moment.
I'm out of the loop on recent developments on the small RWD chassis (been preoccupied). Can tell you the basic premise is to create a new versitile architecture to bolt the Solstice's IRS, front suspension, and drivetrain to (it's NOT a revised Kappa).
The Torana concept was an offshoot of a competition between GM North America and GM Holden to create the structure (NA's version won BTW... Torana's starting point was Zeta). But the size of the Torana is what we're looking at. Pontiac, Holden, Opel (including Saturn), and Cadillac will have models based on this architecture, and the early leading candidate to build them is Wilmington (lots of things can change between now & then, though).
This small chassis will be the basis for sedans and a coupes. It initially started out as a '4 cylinder only' structure, last heard was the idea was changed to accept V6s. GM-Holden sees the chassis as a volume sucessor to the VE. GM-North America sees it as the next performance car chassis.
This is being eyed as a G6 successor. Unless Camaro sales simply flat-out take off (meaning approaching 200K annually) and the coupe market explodes, common wisdom is this is probally the only chance of seeing the Firebird return.