I grew up in a BOP (Buick-Olds-Pontiac) loving GM family. Although I have no real brand loyalty these days, and neither does my family anymore, I want to see them succeed. But I know better. They axed my favorite brand (Pontiac) and aside from Cadillac, the Camaro, and the new Corvette, the rest of their line-up is full of also-rans that are mostly behind the times or just aren't as good as other cars in their respective segments. I'm not saying they build turds, but I'm saying that they could do better, and they don't because they just get in their own way.
Also, they have a history of doing exactly what I said: they will come out with a car concept that enthusiasts ask for,the bean counters get involved, and they release a car that just isn't the same or kill the thing in it's prime. Look at the Fiero. They release a sweet car in 1988 with revised suspension and great looks, and they axe the thing. Also see the new Buick GS. Europe gets the Opel Insignia OPC with a twin-turbo V6 and AWD, and we (up until this year) got a FWD turbo four. The new AWD variant is actually down on power, and only comes with an automatic. I actually like the GS, but it could have been so much better!
Look at Pontiac. At the end, they were slated to become a performance-oriented powerhouse. They were offering a decent roadster (the Solstice) with competitive handling and performance packages, the cool Solstice Coupe, and a gnarly V8 sport sedan (the G8/ G8 GXP). The Cobalt SS should have been a G5 GXP instead. Saturn was even starting to become an American Opel, which had lots of potential. Then poof: they were gone. They kept the brand that was most popular in China.
I have no problems with four door cars, especially new ones (I covet a new Charger R/T), but they will be stepping on Cadillac's toes with this car, and that's just not a good idea considering the present health of the company in whole. They need to make it different somehow, or not waste the R/D time and money on the project at all.
And for the last time, there were no V8 powered GN's or GNX's! They ALL had a variant of the 3.8L V6. The GSX, based on the Skylark/GS of the early 70's, had the Stage 1 455 V8, and were torque monsters on par with the Chrysler Hemi. In the 80's, they DID offer a T-Type with the anemic carbed Olds 307 V8.