If they keep servicing the 3DS as a separate entity, this thing is going to fall on its face. It's an interesting idea with some pretty poor execution, IMO. They would have done better by just recreating the Wii U in a way that the tablet emulated the lower display of the 3DS, meaning you got a single platform with a consistent hardware experience that gave the library flexibility of being friendly for home and portable consoles. Pair it with an Xbox Platy Anywhere system, and they'd have something really nice.
Instead, we've got a lot of unknowns. We don't know if there's touch. We don't know what software support the thing will get from Nintendo. All I know, really, is that Nintendo didn't product nearly enough content (skipping franchises like Pokémon, Mario Golf, Metroid, Zelda, Animal Crossing, and Fire Emblem on the Wii U, while also royally botching Mario Party and Mario Tennis) for the Wii U. They have to get games going, and not just for launch. They can't put out 3 good games, then take a year off. They need to have a steady release of one decent game every 3-6 months, which is a pretty pitiful goal, when compared to what third-party devs bring to the other consoles. Still, that would be enough to make the Switch a worthwhile secondary/mobile console. If they keep treating the 3DS as a first-rate platform, and giving it big-time exclusives that the Switch won't see, then the Switch is going to struggle for entertaining content and get no love.
I won't get a Switch at launch because I don't trust Nintendo will do it right. They haven't in years (considering my dislike for the original Wii, I'd say about a decade). I'll wait to see 3 things before committing to the Switch:
1. A legitimate network for online play (including voice chat)
2. A decent lineup of launch games
3. At least 5 total games on the console I'd want to play (which isn't even true with the Wii U now, for me)