Lets make some comparisons . . .
Olympus PEN E-P1
121 x 70 x 36 mm 355 g
Olympus OM-1
136mm x 83mm x 50mm 510g
Nikon D700
147 x 123 x 77 mm 1074g
How can Nikon turn a D700 into a E-P1 ? they can't . . the depth is constrained by the F Mount Flange focal distance of 46mm, add to that the sensor substrate, PCB, LCD and LCD cover, Nikon have done well to package that into 20mm (77mm is the depth to the front of the prism/flash, it overhangs the mount)
Nikon can't even turn the D700 into a OM-1 in terms of depth.
What about the height ? well the battery, EN-EL3e measures 53 x 38 x 20mm, below it is the battery door, above it are the command dials, shutter release and LCD. The 123mm dimension is not just the height of the body where the battery goes, it is the height to the top of the prism where the hot shoe is . . to turn a D700 into an OM-1 would allow for 30mm of height in addition to the battery . . . that isn't possible IMO.
The width is the closest dimension between the D700 an OM-1 . . that could probably be trimmed.
In summary, why can't the D700 be the same size as an OM-1:
the OM-1 is a manual camera, it uses 2 button cells and a manually cocked shutter, mirror and aperture.
the D700 has a large battery, AF, electrically actuated shutter, mirror and aperture and can shoot at 5fps.
the D700 has a pop-up flash on top of it's prism
the D700 has a large LCD (61 x 46mm) behind it's sensor
can it be made 20% lighter and 20% smaller ? yes it can . . . but that will probably add 50% to it's price, not reduce it.
I guess we will see in due course, lets see if Nikon make a fool out of me . .
As for the shutter/mirror size I am sure you know that we had FF film SLRs in the size of todays m43 cameras (An Olympus OM-1 is as small as todays Oly m43 models). Note also that D300 has exactly the same form/size, except for the prism, as the D700 despite the difference in shutter/mirror size.
So my prediction/hope - a 20 percent smaller, 20 percent lighter and 20 percent cheaper FF than the current D700. The body of the D200/D300/D700 is now six years old, so I bet on the form factor of the D7000.
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