Bob Lutz on diesels, hybrids and fuel cells:

The addition of a second hybrid mode to the drive system improves efficiency, and reduces the need for large electric motors found in typical single-mode systems available today. And we’re putting it on our largest vehicles first, where it will have the greatest effect on fuel consumption.
However, the two-mode system will be scalable, meaning it’s suitable for use in a variety of front-drive, rear-drive and all-wheel-drive vehicles.
In the long-term, GM sees the hydrogen fuel cell as an opportunity to transform our entire industry. Our progress in fuel cell research has been seen before, especially in our show cars the GM AUTOnomy, Hy-wire and Sequel. These vehicles clearly demonstrated that fuel-cell-powered cars can become a reality.