I don't know about that. Lutz has already stated they can't send the Ute here as an El Camino because Chevy already has enough models. There is room for the Impala and G8, with the Impala being LWB Zeta and G8 being SWB Zeta. The G8 can have a higher pricetag, despite it's smaller size, and will be tuned more towards performance. The Impala will still need to stay reasonably priced, so they don't lose all 300k sales that it does now. The Malibu may be able to make up for some of it, but not all. The G8 will be lower volume, and can afford to have a higher price, since the Grand Prix is lame anyway. If GM gives Pontiac a coupe(GTO), and mid-size RWD(Torana), Pontiac would be GM's hottest brand.
If that happens, Cadillac would also be able to use the Torana platform to make a true 3 series competitor.
Buick could offer the LWB Zeta, with a higher price than the Impala, and it can appeal to the DTS buyers who will need somewhere to go once the DTS is killed.
I don't think Cadillac should get Lambda, they should just update the SRX to be less wagon-like, and lose the 3rd row. It's a great vehicle, that is being held back because it looks odd from certain angles, and should never have been stretched to fit the tiny 3rd row.