> Check out an older Pentax or Nikon SLR system.
I have some of those older Nikon systems. The compact SLR's such as the Nikon FG and EM did away with the DOF preview. The Pentax K-1000 and ME did not have it, either. It's not uncommon to pick up an SLR made after 1976 or so without DOF preview. On the Nikon DSLR line-up, it appears that models "below" the D70 do not have it. I am not aware of any Autofocus system that is smart enough to compensate for focus-shift when stopped down. You could make one that does it: but no one would like it as the image would appear to be out of focus through the finder, or there would be an extra lag when you press the shutter release as the body/lens refocus to take the shot.
Back to the C-Sonnar: This lens uses a 46mm filter, and the front element is larger in diameter than the older F1.5 Zeiss Sonnars of the 1930s and 1950s. Those lenses use 40.5mm filters. The larger front element means less vignetting at the edges. As focus-shift is related to the aperture of the lens, and the front element of the C-Sonnar is bigger than the older lenses, I'm guessing that could contribute to a larger focus-shift.