http://www.nintendoeverything.com/34525/ 

their bigger, what could they be hiding under there?

Motion controls mayhaps?

hmmm... doesn't seem like a very good idea to me. If Nintendo wanted to put in motion control, they would just make a new handheld. Possibly expanded storage space for better graphics or longer games. I doubt Nintendo will actually end up using it.

GPS

Remember, I called it xD

I wouldn't be surprised if these were for extra space on the cartridge, but they wouldn't be used until the DS2. I think they'll want to maintain backwards-compatibility, and they won't want to have a separate slot for original DS games, so they'll make them the same shape.

I see that as well.

Possibly just something to make bigger storage DS games. Then again, it could also be possible that they are making a new type of DS cartridge to 'bridge the gap' to their new DS console and this new cart will work on both the DS and DS2. Much like the early Game Boy Color carts. And it just as easily could be a concept and never come to fruition.

you don't need to make the cart bigger for more storage since the size increase significantly for the same space over the last new years.

Rumble and Accelerators.

I'm calling it now.

A propeller will fold out of it and fly you away to a secret island where game characters are real! But it will most likely be motion controls for the DS or something.

VIDEO PROOF OF THIS ACCESSORY!!!!!!!!!!!!!!!!!!!!!!
VIDEO PROOF OF THIS ACCESSORY!!!!!!!!!!!!!!!!!!!!!!
VIDEO PROOF OF THIS ACCESSORY!!!!!!!!!!!!!!!!!!!!!!

http://www.youtube.com/watch?v=qVAU26OxxSc

This is an interview with Shigeru Miyamoto. At 2:05 in the video, he has a DSi in his hand. Attached to the DSi is an accessory that looks exactly like new cartridge. PROOF!!!!!!!!!