The iPad Pro is expected to ship sometime in the first half of 2015, and based on the case which leaked yesterday I would say that is very likely going to happen.
NowhereElse.fr got their hands on a photo of a rear shell which they say was made for the iPad Pro, or the iPad Air Plus as they call it. That site has tended to have good sources in the past, so I tend to believe that this is the real deal.
As you can see in the photo at right, the shell has cutouts for the rumored 4 speakers, as well as cutouts which match with Apple's usual design decisions.
For example, there are obvious cutouts for the headphone jack (upper left corner), lightning port (bottom center edge) and camera (upper right rear shell). Curiously, it looks like Apple may have moved the mike to the long edge (on the left edge), probably to get it away from the speakers.
While there's no way to prove that this isn't an elaborate fake, I tend to think it's real. As I wrote last week, I expect declining iPad sales will inspire Apple to release an iPad Pro.
Furthermore, I was told by several case makers at CES 2015 that Apple does give case makers advance notice of a launch. Several told me that they got a head start on making a case for the iPhone 6 last fall, but were left scrambling to catch up when the iPhone 6+ launched as well (this matches with pre-launch rumors of a possible delay).
I think that's entirely plausible that this case was made from a company with early access and inadequate security, for which I am very grateful.