I recently traveled to India with my Surface RT and I pulled it out of my bag to show them and they made me put it through the x-ray machine along with my Macbook. I would say that it depends on the person at security.Next time I fly I know I won't. It's always been annoying having to pull out the ol' laptop into its own tray. They don't require iPads to be removed, so why should the Pro be treated any different? One more hidden benefit of the Pro???
The Pro might be different because of its slightly larger size (do you really want to argue with TSA?) but I have also left the RT in the bag. It is definitely small enough they see it as a tablet and let it go.
For full disclosure I had the touch keyboard attached. I had a laptop in the tray by itself but I ran a Nexus 7, the RT and an iPhone all through in the same bag without any questionsThe only thing that I think may catch their eye is if the type keyboard is attached. I'm sure in an x-ray they'll see something keyboard-like and may throw a fit.