The basic misconception of most (tech) camera makers is that digibacks don't have manufacturing tolerances, which is obviously not the case. In fact the manufacturers even change specifications from time to time, like changing the protective glass and filters in front of the sensor without notice. You won't have many problems with retrofocus lenses, as they are not so sensitive for changes in the flange distance by design. But each refraction or surface change of the light that's passing through a lens you pay with lesser performance. Retrofocus constructions are unfortunately required to compensate for the mirror box in SLR cameras.
Tech cameras with symmetrical (or kind of) lenses which are optimized for digital capture don't have these issues. But they are significantly more sensitive regarding flange distances or variations with sensor flatness. This goes especially for wideangle constructions. You need to consistently produce with very tight tolerances to be able to reliably measure (and handle) these differences, otherwise the perfect calibration of a system will be a matter of guessing and luck. In there lies the advantage of the Alpa platform, once a back is calibrated you can rely on that it will work perfect on any combination of camera and lens. This might not be too important if your manufacturer offers only one camera, but if you can switch between six models, depending on the job you have to do, it's crucial.
