I see the 3DS to DS as similar to the PS3 to PS2, in that in and of itself, it is performing fine, but compared to its predecessor, it is clearly a major decline. While I don't see the 3DS as "doomed," it's a total step back from what made Nintendo so mass market with the DS, and the sad part is Nintendo doesn't seem to care, as long as they keep cranking out the games THEY like to make, even if they are extremely niche.
I'm not trying to flame Nintendo or anything, quite the opposite. I'm a huge fan and want to see them do well, and as the NES, Wii and DS has shown, they have potential to not only do well, but totally dominate. The problem is they don't seem to care about that. They only want to make the "hardcore" type of games that THEY enjoy making, regardless of the returns.
