The smaller version of the 50MP Sony Sensor in the A7r, shows the same problem with wides on shifts past about 10mm. Crosstalk creating quite a bit of loss of saturation on greens and blues. Some seems to come back in C1 with the LCC processing.
What you don't see any of is loss of detail. I was shifting the Rod 40mm HR-W to 20mm and it held up very well at F8. Same for the SK60.
The SK35 works but can't get the same amount of shift maxing at about 10mm and 8mm is where the cross talk problems start.