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?