[HVM]

Well, Chevy and Cadillac are save and set in right direction. Let´s focus on the grey zone in between. Every brand has a loyoal fanbase who think that their very brand has a right to have resouces to develop new models. For example Hummer fans think that GM has money to fund diesel hybrids and 30 mpg H3 and such. But that´s not gonna happen. We´ve got to be realistic.

Let´s start with Pontiac. Some think that Pontiac should chase BMW. But when GM does not have enough money to fund DT7 for Cadillac, RWD G6 and G4 are notgonnahappen.com.
Others want it to be Holden USA but Holden is a mix of GM DAT, Opel and VE/VM. Here is the problem. I don´t think that a brand can survive with a small, incoherent lineup. You can´t just have a Solstice and G8 and call it a brand. Here is the old problem. Overlap. This time with Saturn. You cannot have two brands with Opel based lineup. Fine, choose one. Pontiac should stay because its image fits Holden´s better, can succesfully sell opels and VEs, has more dealers and is sold in combined B-P-G stores. With Saturn gone, Pontiac can take GMC´s role as a volume line of B-P-G.
Pontiac in my vision is a sport performance brand, a half step above Chevy, but still mainstream, set to compete with brands ranging from Mazda, VW, Kia to Subaru. Here is my lineup:

G2 (Opel Corsa, H3/5)
G4 (Opel Astra, sedan, H5, cabriolet)
G6 (Opel Insignia, sedan, coupé)
G8 (Holden VE, sedan, wagon, ute)
Solstice (as is, coupé, roadster)
GTO (Holden Monaro, coupé)
Vibe (Opel Zafira, MPV)
Vue (Opel Antara, CUV)

With Pontiac as a volume leader, Buick can be the niche brand. I like the description of understandable american luxury. I vote to keep this brand for obvious reason (China). My lineup:

Invicta (lwb EpiII sedan, Lexus ES killer)
Riviera (Zeta coupé, cabrio, Lexus SC killer)
Electra (lwb Zeta sedan, Lexus LS killer)
Enclave (as is, Lexus RX killer)

GMC. Well, I don´t thing it would be worthy to kill it. Let them be the professional grade.

Jimmy (GMT-700 SUV, size to compete with Wrangler)
Sonoma (GMT-700 p/u)
Yukon XL (as is)
Sierra (as is)

Sell Hummer.
Sell Saab (don´t like this but GM needs cash; sell it to BMW or PSA, not to China, please)

This leaves you with three sales channels:
Chevrolet, Cadillac and B-P-G in between, when Buick is Buick China, Pontiac is Opel and Holden and GMC is Chevy. It is a clear structure applicable worldwide. For example in Europe you have Chevy - Opel - Cadillac, in ME the same as US.