The device is a successor rather than a redesign of the current system; recent rumors have suggested that Sony is also working on a redesigned PSP. It is not clear if the two rumors are in fact speaking about the same project, but this new report definitely refers to a brand new system. It will have built in hard drive support from the beginning, and will not be using the UMD media format, either for games or for other content.
Sony developing PSP 2

Shacknews claims Sony is working on the PSP2: