[sho]

That's not how depth of field works. DoF, simplistically, is governed by the usable angle of light at the back of the lens - the more obtuse, the more "DoF". Larger sensors (like your 6x7) might be useful if there are limits in sensor resolution, necessitating the sensor being placed further back so the light can shine over a larger area. But if the sensor is higher resolution (as I said the 645z is 50MP) then it can be closer and capture the same DoF. If technology improves enough then we might be able to deliver your "medium format" DoF with a 10mm*10mm sensor placed right up close to the lens. You would not be able to tell the difference.

The 645z and x1d are delivering the medium format DoF right now. Things can be improved upon, sure, but insisting on a certain sensor size is misguided. That size was necessary simply because of the limitations of film chemistry. Remove this limitation and the sensor size becomes less relevant.

[ekianjo]

No. DoF is also a factor of sensor size/film surface area.

https://en.wikipedia.org/wiki/Depth_of_field#Relationship_of...

http://www.uscoles.com/depthoffield.html