We've seen people mounting cameras together side by side to produce a 3D videos.

Would Nintendo go that far and implement 4 cameras into the 3DS?

doubt it to expensive lol

And it'll be made of PURE GOLD.

Cameras can make for a pretty cheap component nowadays, actually.

All the same, I don't really see the payoff. It would take a lot of processing for the device to "see" 3D, and it won't be an effective input method for a device you hold in your hands.

This is most likely the technology behind the 3DS LCD...

I meant more than just the price of the cameras there will be other costs involved for a start there is the processing and then there is storage (recording two video streams) and you need decent amount of ram and will need 3D video codecs and probably basic video editing the list goes on. And the trade off like you said there isn't that big anyway so the cost to benefit ratio isn't that good, you may see it on a hardware revision like the DSi tho.

That or if they were smart about it, the could have the camera's in the hinge and flippable both directions so that you could have a camera each way, or two camera's either way, so that 3D photo or video is possible.

Yes, that's the screen 3DS will use

Well in that case, right you are.

maybe 3
2 on one side to capture 3D images, and one on another for 2D images

3DS=3 Cameras

3DS= 3D image capture

3DS= 3D gameplay

3DS= TRIPLE THE FUN!!!!