Yikes:
Canon develops APS-H-size CMOS sensor with approximately 250 megapixels, the world’s highest pixel count for its size
Canon Inc. announced today that it has developed an APS-H-size (approx. 29.2 x 20.2 mm) CMOS sensor incorporating approximately 250 million pixels (19,580 x 12,600 pixels), the world’s highest number of pixels1 for a CMOS sensor smaller than the size of a 35 mm full-frame sensor.
When installed in a camera, the newly developed sensor was able to capture images enabling the distinguishing of lettering on the side of an airplane flying at a distance of approximately 18 km from the shooting location.
I’d imagine that a limit on the utility of the system would be the optics. I know dialing in focus for long-distance shots is troublesome enough with my creaky old camera now… I shudder to imagine the utter failure of getting precise focus for a 250 megapixel sensor.