The system will be released before the end of the fiscal year, which means the latest we'll see it in Japan is next March. The system is expected to make an appearance at this year's E3, and we'll surely be given more information before then. For now, Nintendo has yet to release any images of the system, or how games will look, or be played.
So how will the 3D effect be displayed? We posted a video of a downloadable game that's out now in Japan that uses head tracking to simulate a 3D image, and since then we've had time to try the game on a friend's Japanese DSi during GDC. By tracking the motion of the system in relation to your eyes, you seem to be able to peer "into" the picture by turning the system this way and that. It's a surprisingly effective effect, and some iteration of this system may be used in the 3DS.
Nintendo has a history of announcing hardware upgrades and features that may seem silly at first glance before going on to become huge success. Many scoffed at the idea of the Nintendo Wii, until lines to play the system at its first E3 showing stretched around the convention. 3D is fresh in the minds of consumers after the success of Avatar, and 3D-capable televisions are expected to make a splash at retail this year. A portable system that works with all your old games and won't require glasses? It could be the right product at the right time.
Source: Arstechnica.com