The problem with this is the limits of human attention. It's hard enough to maintain focus on long drives as it is; if the "enhanced cruise control" takes over the job entirely, the driver will have nothing to do and is likely to stop paying attention to the road at all. Then he'll either miss his chance to take manual control, or do so in a state of panic.
Google has been making arguments along these lines -- for instance: http://gizmodo.com/why-self-driving-cars-really-shouldnt-eve...