NS will fall behind the DS as it enters its beast mode (i think this is the time frame NSMB and DS lite released). Also the Wii will grow the gap more, so the NS has no chance until a couple of years later to really start making ground on the Wii (if I remember it sold above 20 million units in 2008 and 2009).
The NS's real battle at least for the short term is with the PS4. It has a chance this holiday season to make an impact.