Erik. Why is that so? And why should it not be possible on a Sony?
It is definitely possible with/on a Sony but for several reasons it's an unlikely route for Sony and for third party lens designers.
Price, the Leica M lenses are super expensive, around three times that of Zeiss. The cost goes to cover the Leica M philosophy; Range Finder, simple to use, very compact, discrete and super high image quality also a more or less manual production line... designing and actually being able to produce in small series, lenses with floating elements that small and with so tight tolerances is no easy task...
The lens and camera/sensor is an integral designed part for Leica, the micro lenses, extremely thin sensor cover glass...
These are also why they keep getting into trouble.
M8 IR issues, M9 sensor cover glass corrosion etc...
But apparently Leica gets away with it despite the prices and the hick ups...
Sony is aiming at super high technology with all the bells and whistles; super auto focus, WiFi, tons of special functionality in the menus, etc... sure they want compact but not that small... and not at the price
Zeiss aim for super high image quality, but are not able to cut the size and weight at the price level they are on, to be competitive with the original manufacturer prices...