[K Dawg ONE]

How about keeping Chevy-Caddy as a 'singular brand' and PBGS as the alternative to the 'singular brandd' and becomes 'GM Collection' or just General Motors? Basically, GM would be down to two channels.

General Motors (with GM being the brand, the PBGS being the modle, and then the trim level):
GM Saturn 'Z' (hybrid hatch - Delta)
GM Saturn 'S' (hybrid small sedan - Delta)
GM Saturn 'L' (hybrid full/mid sedan -EpII)
GM Pontiac 'G2' (2 door coupe/4 door hatch - Delta)
GM Pontiac 'G4' (mid-size sedan - EpII)
GM Pontiac 'Solstice' (2 seat convertable - Kappa)
GM Pontiac 'Firebird' (2+2 Sports Coupe - Zeta)
GM Buick 'Regal' (lux mid-size - Sigma)
GM Buick 'Park Avenue' (lux full-size - Zeta)
GM Buick 'Enclave' (full size cross-over SUV - Theta Premium or Theta-Epsilon)
GMC 'Sonoma' (x-cab pickup - Theta)
GMC 'Sierra' (same configs as now, minus Denali and hybrid)
GMC 'Terrain' (entry level cross-over SUV - Theta)
GMC 'Yukon Denali' (full size cross-over SUV - Lambda II)

Chevy-Caddy would be:
Chevrolet 'Beat' (compact 3 door hatch - GMDAT-M / M300)
Chevrolet 'Cavalier' (3 door hatch/4 door compact sedan - Delta)
Chevrolet 'Malibu' (mid-size sedan - EpII)
Chevrolet 'Impala' (full size sedan - Zeta)
Chevrolet 'Camaro' (2+2 Sports Coupe - Zeta)
Chevrolet 'S10' (x-cab pickup - Theta)
Chevrolet 'Silverado' (same configs as now)
Chevrolet 'Equinox' (entry level cross-over SUV - Theta)
Chevrolet 'Tahoe' (full size cross-over SUV - Lambda II)
Caddy 'CTS' (lux mid-size - Sigma)
Caddy 'DTS' (lux full-size - Zeta)
Caddy 'XLR' (2 seater Sports Coupe - Zeta)
Caddy 'ESV' (full size cross-over SUV - Lambda II)