Frenske: I never understand why people including reviewers comment that it is something short of miracle that a full frame sensor can exist in a body so small. Perhaps they keep forgetting that 35mm film was the standard "sensor" for decades in simple compact point and shoot cameras. Especially if you think about how much space the film roll and the winder took.I think there is a gigantic market for RX1. Maybe Sony can be bring out a compact RX10 with an APS-C sensor with fast zoom-lens.
Unfortunately its not that straightforward. The efficiency of the individual photosites on digital sensors falls off dramatically as the angle of incoming light rays diverge from perpendicular. This was a huge issue for Leica when they introduced a full frame digital M.
The geometry of light paths exiting wide angle lenses means they intersect with the edge of sensor at very oblique angles. It is a minor miracle that Sony and Zeiss have been able to figure out how to capture edge to edge quality in such a compact body where the rear element of the lens is so close to the sensor. There is some very clever software in the RX1 dealing with this problem.
While 35mm film does not suffer nearly so much from this problem its does occur. My old Contax G2 shots benefited from using a center filter with wider angle lenses. The center filter balanced out the light falloff caused by the loss in incident light intensity at the edges of the frame.