This sigma announcement is dated late 2007, but the first pieces are coming in Italy at beginning 2008.
The lens itself aims to be a 3rd party addiction to the nyche of fullframe fisheyes for APSC digital cameras. Not a so much populated place, indeed, if you think the others are the 10.5mm Nikkor f2.8 and the Tokina ATX-pro fisheye zoom 10-17 f3.5/4.5, that is marketed also as Pentax and Schneider.

Well, Tokina is a fisheye zoom, and makes cathegory on itself, let's say its quality, flare resistance and sharpness are so god that can revail with Nikon 10.5mm f2.8.
The Nikon lens is widely used among Nikon and Canon users, who need a special adapter and a piece of plastic to jam the iris mechanism in the desired position.

Let's ask ourself who and how will use this lens.
Fullframe fisheyes are used by creative photographers and sport photographers mainly, since the advent of digitally remappig projection, also wide angle enthusiasts and panoramists became interested in, and I'd say they are the most emanding and the most technically skilled ones.
In the first case they are forgiving everything about real field of view, chromatic aberrations and resolution, and they say "OK, a fisheye is distorting itself and geomtrical aberration are not in count".
We, panoramic photographers really CARE. A fisheye is following its own geometrical projection rules, we call distortion something that is going against that rule. We are picky also with chromatic aberrations not following radial or linear rules, as well as flares, and we WANT to know how many degrees a fisheye can spot. Even more with APSC fullframe fisheyes, cause we like to modify them, shave them ad use them on fullframe, 24x36mm sensor-sized reflex cameras, to shoot spherical panoramas with a small number of shots.