It won't beat 3DS. It might crack 40m. Even that might be lucky. Trying to convince people that a 720p tablet is worth $399 (rumored) will be the hardest sell Nintendo ever does. It won't have access to ios or android. If you look at the reveal video it doesn't show any functionality outside of video games. And according to some here, it won't even have a touchscreen and you will be required to use the controller nubs to navigate the OS.
So why would the average consumer buy a 720p tablet with no touchscreen at such a high price?
This. I think it would be suicide for Nintendo to not put in a touchscreen, but that hasn't stopped them from making some bad decisions before. I still think it will end up having one, cause even Nintendo has to know they can kiss casuals goodbye if it doesn't have one. The biggest thing that will hurt them is they are trying to break into the tablet market, one that already has a clear winner. And people who prefer to game on tablets also like them for their myriad of non-gaming uses, something the NS won't have. And with the weaker HW, core gamers won't be interested in it.
Of course, one of the largest factors is 3rd party support. I think a lot of devs are going to be taking a wait and see approach to the NS. If NS sells well, they will probably start supporting it. However, if it doesn't, it'll be dropped rather quickly. It doesn't help things that the NS is probably ~1/3 the power of a PS4, meaning devs are going to have to figure out how much they have to trim things back to get their games to run at least decently on the thing.
Nintendo HAS to price this thing for $249, with $199 being the sweet spot. If they think they can price it at $299-$399, they got some heartache coming their way.