It looks like the 3DS Circle Pad attachment isn't just related to Capcom. In their latest Kojima Productions podcast, it was confirmed that at least one team at Konami has the Circle Pad attachment. Here's what the group had to say about it.

“I saw it today in the office. I mean I’m sure it’ll enhance gameplay… it’s a little big.” – Christopher Johns
“It feels good I think… it feels good. It’s just it’s an add-on, so I think the only concern is how will that kind of split through the users. Because there are people who are gonna wanna just carry around a really portable 3DS and then maybe only the really hardcore guys want to play some FPSs on there or something will maybe want to get that attachment.” – Sean Eyeston
“I don’t know if people want to carry it around, right? That might be the tough part.” – Christopher Johns
“It is kind of big.” – Sean Eyeston
“I think it adds a new level to gameplay, so it’s definitely worth it.” – Christopher Johns
“Gameplay-wise I think it definitely adds a lot. It’s just size-wise and I guess aesthetics, right?” – Sean Eyeston
“For those who do play for long periods of time, I think that will win over a lot of people…” – Christine Kogure

Could this be why Metal Gear Solid: Snake Eater 3D was delayed? A second circle pad would certainly come in handy for that game.