Unlike previous rumors, which indicated an iPad Pro with a 12.9-inch display, the latest word is saying a 12.2-inch display, on a chassis that is as thin as the current crop of iPhone 6 smartphones.
The design language may not share so much with the smaller iPad siblings, the iSight front facing camera may resemble the set up seen on a MacBook Air, and the TouchID sensor may not be inlaid in a recessed home button. The divergence with the iPad Air 2 may continue with a pair of front facing stereo speakers and dual-array microphones.
If Apple were going to position a tablet against the Surface Pro 3, it would need to be less like an iPad Air 2, and at a minimum a change in the iOS user experience to make proper use of all that screen space, something that would appeal to the business and student clientele of the Surface and current 2-in-1 devices. The new rumors gave a nine month window in 2015 (first three quarters) for a release.