Exactly - and that's the for CTS, a much bigger product on Alpha. When the Camaro becomes an Alpha, this is how it will loose that weight. And all the parts that would otherwise be too expensive for the Camaro pricepoint, such as the aluminum powertrain cradle, are "free" thanks to sharing of such components across the platform.
The Alpha platform was developed with a "gram strategy", where each part was carefully examined and optimized. Even bolts that can be smaller, without giving up the strength called for by their purpose, were sized specifically for the job. And because Alpha is a brand new platform, each component's attributes could be measured against the whole, and contribute to improving the whole.
You can't do that kind of work on an existing platform. As an example the work done to upgrade the Zeta platform in Australia for the new Holden Commodore couldn't achieve these types of results.
So it's perfectly feasible that the next Camaro could drop several hundred pounds, while significantly improving structural integrity. This will translate into a considerably improved HP to weight ratio, better fuel economy, better safety, and a better yet platform for further models and modifications by owners.
We'll have to see what the overall size of the car will be, once spy photos start showing up. But the potential of Alpha is huge and it's there for the taking.