I don't personally know of any cars that put the buttons for dash information in that spot. BMW puts it on the other stalk, so do a couple others I have driven.
That said, many cars put the wiper controls where this little shifter thing is on the MB. My wife, in fact flicked it up the other day while stopped at a light, because this is how the wipers on her X3 worked. The car went directly into reverse. This scared me some, and I knew it was likely to happen at some point when we bought the car.
To answer your specific question, I do not know for sure, but the manual says the car will not automatically shift into park above certain speeds when the door is opened, but I do not recall what it said about the actual activation. Theoretically it should let you do this...it is an emergency stop mechanism that I believe is mandated by law. If it is anything like a normal automatic, it wouldn't stop you immediately, but it would "ratchet" to a stop so as you don't loose control by locking up the wheels.
That said...With the placement of the button, I would hope that there is some sort of verification that you really meant to do this before it happens.
I tested the car out with shifting into reverse while moving (after my wife did this while stopped). The manual seemed to imply that there was nothing to stop you from shifting into reverse while moving forward even though I can think of no valid reason you would ever want to do this.
My testing determined that below ~5mph it will let you go from D directly to R while still moving forward, and vice versa. At these speeds it is likely not going to harm anything. Over these speeds clicking the shifter all the way up only resulted in the car going into neutral. Not awesome, but not terrible either. I did not try pressing up again to see if it would let you go into R if you really meant it. (again, to my mind there is no reason this is a valid scenario, so I would hope they just don't let you do it.) If they do let this happen, it would likely damage the car, so I wasn't willing to test it.
