A scanner lens could be very simple if you use a super strong backlight to get a small aperture and use a peaky RGB backlight exposing sequentially, combined with a monochrome sensor, so remaining CA is more easily corrected in software.
You just invented... a drum scanner!!!
Scanner lenses are probably much easier to design, because they don't need to work with a wide range of magnifications and they are only required to image to and from a really small field.
The film and scanning head transports are more of a challenge.
The hard thing in a scanner (and that hasn't changed significantly with the advancement in sensor and lighting technology) is to ensure perfect alignment and no vibration (with all the transport and autofocusing mechanisms in place) at all time during scanning.
Some folks at Plustek thought they solved this by using a lens with smaller aperture to get larger dof (so to be able to get rid of AF, get fixed film plane). It didn't work out that great. In their second version of 120 scanner they still needed to enable some manual adjustments of film plane to get acceptable resolution. And smaller aperture in scanning lens meant less resolution which they needed to compensate with sensor with more pixels which brought a problem of needing to scan at native sensor resolution to get half of that (oversampling) in the end as real/effective resolution.
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