Whoever threw the idea out there - about that mystery square on the Wii U controller being a vitality sensor - probably(and unknowingly?) hit the nail on the head.
I'm not one that indulges in baseless speculation, but it turns out that the DRC vitality sensor idea may not be as farfetched as initially presumed. I scanned a few paged of this thread and apparently no one posted the connection, so I guess I'll do it.
(don't kill me if I'm late with this... this thread moves too fast sometimes)
Seeing the actual sensor(black square pad) within the vitality unit is so tiny, a lot of the bulk(entire top portion) is most likely just for aesthetics and ease of use, with the circuitry housed in the bottom half of the unit. Therefore, what you may be seeing on the DRC, is likely a refined design of the vitality unit, revealing the only area that needs to be exposed - that tiny square "contact pad".
Now, mind you, this is a speculation thread, and this is in no way conclusive evidence, but it damn sure seems more of a possibliity than before. Also, consider how silent Nintendo have been about this peripheral they were initially so excited about. Would they just let the concept (that was in it's completion) die, or implement it in their next system? I guess we'll find out in a couple weeks!
Note: The other "mystery square" next to the power button appears to be a button(rather than a "pad"), and will most likely differ in purpose from the square "pad". I also do not believe it's a sync button as some have speculated, since the red sync button was spotted at the back of the E3 2011 controller. Although Nintendo could have changed the location of the sync button in the updated version, I doubt it's at the front of the controller. If the Wii console and wiimote is any indication of Nintendo's current train of thought, they'll perfer to keep the sync button "hidden" at the back or under a flap, to prevent excessive/unnecessary use. Of course, I could be wrong, but, that's just my take.
PS: While I prefer to lurk, I do follow this thread, and you guys have provided me with tons of entertainment while I wait for E3. Whether by thoughtful speculation, "insider tidbits", digging for clues, or simply hilarious gifs... well done Nintendo GAFers!
That's possible, but wouldn't it make more sense to place it on the side then? Where the palm is in constant contact?