The key thing would be to compare the picture quality of this new D100 with the SD-9 of Sigma which uses the new Foveon 3x chip which is supposed to be way better than traditional CCD's capable of higher ISO ratings without noise typical of traditional CCD's.
Basically with Nikon they have an agreement with Kodak to use the F5 body as a platform (don't know when it will expire) So the D1 series is based primarily on the F100 body and the D100 primarily on the N80 body. Although true that it is not just a graft on of a digital back, the casing and design is basically apparent.
The D100/N80 body for those also familiar w/N80 body, - Pop up flash - As the other lister noted CAM900 instead of CAM1300 of F100 - and display grid. - The controls to switch metering mode and AE/AF lock is the same as N80 - The APSM control knob on the left side of camera is also from N80 - The Low light focus assist light - From N80 - No metering using manual AIS lenses - From N80 - Same camera strap attachments as N80. - Revert to use of manual srew on remote cable shutter release - From N80 - Optional use of 10 pin data with Multi-function battery pack only for use with ML-3 or MC-20 and other data exchange. - Smaller grip and plastic Body. - Rectangular view finder - built in diopeter from N80 - No optional diopeter lenses or angled view finder can be used.
To call it based on the F100 is really false advertising to me.