it probably will.
The 3DS, which wasn't that impressive in itself (although I like mine) may end up crossing the 70 million mark. It wouldn't be THAT impressive for the next partially handheld Nintendo device to retain the 3DS fanbase and then when you add in those interested in the home console aspect....
I think the strongest reason it may end up with quite a large userbase is going to be the game library. People in the past at times who aren't big Nintendo fans seem to be torn- do they buy the handheld OR the home console? in some cases it was literally a decision of buying one seperate game library vs another. And the confusion and decision making I think would cause people to go with neither. It can be daunting, the idea of having to buy two systems to get access to a lot of great big N games
with a unified consistent game release schedule one should expect this system to sell well.
Also price point wise 300$ (or even over) would be perfectly fine, this is a 2-1 device. People spend 700$ on new phones. Be realistic here folks. Adjusted speaking a lot of the older consoles would be like 500$.