I'm not even reading your post to tell you no, it's a stupid idea.
High Country is too regional in appeal and nobody outside of the midwest and under 50 will buy a "Cruze High Country" or anything of the sort.
No.
Chevrolet sort of has a brand with LTZ... but it's just a trim. Just like Denali, at this point.
No, it doesn't.
Chevy is Chevy, GMC is GMC. Brand separates them. Same principle as Buick NOT complementing Cadillac's lineup, they're two completely different brands.
Chevy and GMC are less defined, so there's more "danger," but not really. They're within spitting distance of each other in the price of everything, and luckily Chevy has such an abysmal image in some circles that people will buy a GMC because it isn't a Chevy... even though they're basically the same thing.