People complain now, that dslrs are too big and thick. If you tilted the back, as in that Spanish mockup, the camera would be even thicker.
The sensor MUST be perpendicular to the lens axis. That's simple physics. You can't change that, at least not with any technolocy available today. Therefore, the sensor plane can be no further back than the bottom of that sloped back. All that extra space behind that plane at the top of the camera is in addition to the present thickness.
IOW, you could take the existing camera back, pivot it around the BOTTOM edge of the camera and tilt it back 1/2 inch or so. You can't pivot around the top edge and tilt the bottom IN 1/2 inch. That would move the sensor too far forward.
So, a sloped back would only make the camera noticable bigger than it already is.
Besides, I've never been bothered by having my nose against the camera, either with my film slrs or with my K10D. I do have to periodically wipe the nose prints off the back LCD, though.