My biggest concern with the Switch is it will launch with just a bunch of "definitive edition" Wii U and third party X1/PS4 ports. I think the system itself looks like a major winner and far more appealing than Wii U ever was, but none of that will really matter if it launches with just the same games you can play on Wii U. Then it's not going to seem like a new system to a lot of people. Having the Mario game in the trailer ready at launch would be a huge coup, but I highly doubt it's that far along in development. I think a delay to q3 or q4 would be far smarter if they don't have a few good exclusives ready at launch, and I highly doubt they do given a few seconds of a Mario game is all we saw for a new exclusive in that trailer.
The other concern would be pricing. Nintendo has branded themselves on being the "affordable" option for well over a decade in the industry, however this thing is essentially an iPad, home console, and handheld all in one. Considering that I don't think as high as a $400 price point would be unreasonable, but the public certainly would given Nintendo's image in terms of pricing. So that could be a problem too. Honestly I'd be surprised if it's feasible to launch this thing for as low as $300, but that's what people are expecting. So I'm worried about that.