Nintendo didn't talk about the 3DS control add-on at their conference. Like, at all. And there are no first party titles that take advantage of it. I don't think it's a major part of their 3DS strategy, guys. (So, no early-adopter-screwing quick-and-dirty system redesign.)
It hits December 10, the same day as
Monster Hunter Tri G, for 1500¥ (about $19). It will probably be bundled with some game(s) for 1000¥/$10 more than regular price. The short list of games that take advantage of it is basically the console-style "core" games you'd expect:
Resident Evil: Revelations, Metal Gear Solid 3D, and
Kingdom Hearts 3D. No announced games require the add-on.
It's just a Classic Controller redux. Now that we have that out of the way, the deets: It apparently communicates with the 3DS via IR — so
that's why they brought back the IR port! — and requires 1 AAA battery. It's model number CTR-009, and it only seems to be available in black. And there's technically no word of an international release yet. So there you go.