I don't notice anyone else doing this, so I might as well go for it: This was an earlier version of the controller.
Why do I believe this? Gather round the campfire, kids, Peanut's got some theorizin' to share.
You may remember some patents being made public around late February where the Upad (as I'll call it) was pictured as having analog sticks. You can see them pictured in this article. In the articles that presented these photos, these were accompanied with the claim that Nintendo originally intended for the Upad to have dual analog sticks and not circle pads. It's said here that the patents were filed at the time of E3 2011, but it's possible those designs were the functional build and not the conceptual one. Fast forward to Friday where we saw a patent that shows wiimote-Upad interaction, and the one pictured resembles the Upad from E3 2011. Katsuya Eguchi, a senior video game designer at Nintendo, has also stated that the company believes circle pads are the aesthetically and ergonomically superior form of analog control. Granted this was back in July, but it was after the E3 conference. While Nintendo may be just showing the old model to keep the new one in secrecy, it's also possible that the pictured model was actually done away with and the model we saw is basically the model we're getting.
With all this in mind, I'm very hesitant to believe Nintendo would bother returning to their old design when they believe so strongly in the opposite choice. Sure they changed their tune pretty quickly about the 3DS in a few cases, but this doesn't appear to be one of those cases. I don't, however, doubt that this was an actual version of the controller at one point, and I believe it explains why the employee on Twitter felt safe posting a photo of it. They assumed that Nintendo would be less likely to react to an older version of the Upad being posted than the current build of the Upad being posted. Based on how quickly the photo was taken down, though, Nintendo clearly treats any hardware leak equally.
So what do I think of this? While the sticks might have offered a kind of precision the circle pads can't, the CPs fit better with the build of the controller. Having a consistently flat surface would be less cumbersome than having these two sticks popping out, and they would lend themselves better to clicking if those rumors turn out to be true. Another reason I'd be happy with this outcome is that the E3 2011 button layout is far better spaced, the only potential advantage of the old one being the diagonal placement of the right stick (but that ultimately comes down to personal preference). I do hope Nintendo keeps the LED notification system that's very evident on the pictured controller's home button.