It seems that the new iPad Pro model of 10.9 inches of iPad will have the same footprint as the current models of 9.7 inches, thanks to the much thinner bezel on the sides of the device.
A release from the Japanese site Mac Otakara reports that the device will also be slightly thicker than the existing 9.7-inch iPad at 7.5 mm and the iPad Air 2 (6.1 mm), keeping the same thickness as the iPad Original Air.
According to sources "informed" Mac Otakara told that the device will retain the top bezel where the front camera FaceTime. Somehow, the classic start button should be removed, although the report does not specify how Apple plans to replicate its functionality.
The Cupertino company could replace the physical startup button either with a virtual button on the screen, or by an "embedded" startup button on the screen. Just the last option, probably applied in the "iPhone 8" next year.
As for the thicker iPad Pro, the space could be used to accommodate a larger battery, an additional layer of the screen that contain a sensor array 3D Touch, a higher resolution screen or other hardware additions still unknown.
Interestingly, Mac Otakara mentions that the 12.9 - inch iPad Pro will also be affected by increased thickness in about 3 to 7.2 mm, versus the current iPad Pro that has a thickness of 6.9 m (iPad Pro of 9.7 inches has a thickness of 6.1 mm).
Finally, the report points out that a forthcoming 7.9-inch iPad Pro model will replace the current 9.7-inch mini-iPad. It is believed that this device will have the same size and thickness as Apple's small tablet, as reported by Mac Otakara sources.