On a sidenote, the DS has distorted the perception of people. I think the peak year for a non-Nintendo system in Japan was only in the ballpark of 4m. But here we are and call 5.5m "respectable".
I don't think the 3DS will beat the DS's record, but lifetime sales in Japan are a different story. If third parties drop the PSV, then the 3DS will have a much longer tail than the DS.