That's odd. I thought Sony was "supposed to" have taken wide angle M lenses into consideration when designing the A7r. And the A7 was the one that was going to exhibit issues with the wide M lenses.
A voice from the past jumps back in the water. I figure I'm allowed back here now that I've sold my D800 and heavy glass (well in a few more hours I will have).
I can't find anywhere that categorically states Sony set out to design a camera capable of supporting every single M lens under the sun without any colour shift or smearing. Heck, not even Leica can claim that.
Instead, I believe and have believed for more than a year now when it was clear to me that Ricoh had given up on this slice of the market, that no one, other than Leica, is likely to ever again produce cameras tuned for M lenses. As sensors get larger the problem becomes more difficult. Instead, makers are quite right to develop new designs or refine old ones such that they can more easily handle the demands of a full frame sensor.
Indeed that's exactly what Zeiss are doing - they've announced they'll build a new line of manual focus lenses specifically for full frame mirrorless cameras like the narrow back focal length E mount, and the first platform they'll support is E mount. Leica have been and will continue to refine their own designs for better "digital" compatibility, which really means full frame sensor and increasing pixel density compatibility.
The new Sony FE 35/2.8 shows that Zeiss design can produce a compact, very high performance, full frame lens that delivers sharp results to the periphery. It has quite a different design than the Biogon 2,8/35ZM.
Here's a film-era Biogon, the ZM 35/2.8 (which needs another 9.5mm adapter added to it for E mount use):
(Source: Zeiss)
Sony on the other hand has no legacy to cater to. The Sony FE 35/3.8 shows you can design a lens that is, like the ZM35/2.8, of small size, but preforms solidly on big digital sensors.
(Source: Zony)
While the above isn't built to the ZM standards, reportedly it is built very well.
Those that want the traditional ZM type of all metal manual focus RF style lens -- probably with electronic contacts for E mount (yay, EXIF data) will get their wish in an updated E mount version sometime in 2013.
I see these types of developments as a positive. Sure, I wish all existing M lenses could run on any camera under the sun, but I became convinced this wasn't going to pan out that way, at least not until some quantum leap forward in sensor tech happens. I felt so strongly about this I sold all my ZM glass off early in 2013. The Zeiss announcement kinda convinces me that nothing like that is on the near horizon.
In the meantime, I'm going to be an A7r guinea pig using 2 native Zeiss FE lenses and filling in the ultra wide end with something adapted until native lenses fill that gap.