I don't typically pay much attention to rumors until they start being released more frequently and closer to the expected launch date. However, this one concerns me since it was released by Sonny Dickson. If memory serves me correctly, he has typically been accurate with his leaks. I hope, as others have said, that this is a fake design schematic to throw people off or that there's possibly a different purpose for that cutout. I have to agree with most that the placement of Touch ID on the back would be poor placement. If it's not ready to be implemented under the display, leave it where it is. I'll gladly opt for convenience over a larger screen until it's ready to be done properly.
On the upside, the sides appear to be flat like the 5S which would be a welcomed back addition. The curved sides are just too slippery.
As another poster alluded to, it would be kind of funny to see Apple include keynote slides showing us how Touch ID was moved to the back only to have the next slide say something along the lines of, "You didn't really think we were going to put it on the back, did you?"