According to a report on Nowhereelse, via BGR, it looks as though the first picture of a protective case for the forthcoming 12-inch iPad Air Plus/iPad Pro has leaked.
Examining the picture closely, you can see that it is definitely not for the iPad Air 2, as there are subtle differences in the placement of various outlets.
For example, you can clearly see the four cutouts in each of the four corners of the case, which could be the site of the four speakers that the iPad Pro is expected to have.
This would appear to be the main difference, as other cutouts shown on the case are similar to those for the current iPad Air 2, such as the standby button at the top, rear camera housings, and the volume buttons.
Another somewhat mysterious cutout can be seen on the right side of the case, and as yet no one has come up with a good idea of what that might be for!