[Number 3]

A great point, but the main issue with keeping a Gen6 running 20 or even 30 years from now is the production numbers. Basically, they didn't sell enough to warrant the aftermarket community tooling up a lot of parts. Now you can get aftermarket headlamps and taillamps now, but none of those are OEM quality (regardless of what they tell you) but down the road you may need things like front or rear fascias (available today) and sheet metal (not likely down the road) or interior bits (also not likely).

If you want a taste, go out and look at a few other low volume cars GM has done and see how the parts availability is. Pontiac Solstice/Saturn Sky and the Chevy SS. Solstice and Sky are 15 years past end of production. SS is pushing 10 now. I've not heard great things on Solstice/Sky parts. Gen6 is higher than these examples, but it's sales volume that will help the aftermarket tool things up down the road.

And since it hasn't come up, there is no requirement for 10 years of parts availability. It's kind of an urban legend but isn't a requirement anywhere. Some companies do try to keep service parts on had, including body panels and cabs for some time after production ends. I remember at my first job at GM we were building out for service cabs for the old MD tilt cab.