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I also prefer the classical construction, but I am guessing that this is an attempt at weather-proofing. The lens looks quite sealed.
Looking at my bad snapshots of the Photokina prototype, I’m convinced this lens will not be given a glass cover over the distance scale unless it’s substantially redesigned – which I think unlikely.
First, there’s nowhere for the glass plate to attach. It can’t very well attach to the focus ring!
Second, many popular lenses over the years have used an arrangement like the Distagon prototype, including enormous numbers of Pentax lenses – lenses which if anything are famous for their high construction quality, smoothness of operation, and longevity (I have a 30-year-old 50 mm f/1.7 that is extraordinarily well made).
Third, there’s no point: it’s already sealed as well as any manual-focus lens, which is to say more than adequately courtesy of small gaps and grease in the focusing helicoid. These lenses are more impervious to weather than supposedly sealed autofocus lenses, and less likely to suffer permanent damage if they do get soaked.
And fourth, there are good reason not to add a window: glass or plastic can break, plastic scratches, and any material reflects light, which can sometimes interfere with reading the distance scale. And with those cine-style neon yellow (fluorescent?) markings, Zeiss clearly cares about readability here.