A photo of what looks to be a possible iPad Pro industrial prototype was discovered on Chinese site Weibo.com by French site Nowhereelse.fr.
The photo shows a very rough rendering of what appears to be an aluminum back plate of a very large iPad casing. You can see an etched circle at the top left for the rear facing camera and an Apple symbol in the middle. Though it is impossible to determine the precise measurements from the picture, it is clearly larger than the 9.7" iPad Air. It isn't clear where the specifications for this mockup came from so, as always, don't take it as gospel.