If it's a 3DS successor, I can see it. 3DS sales peaked in 2012 and 2013, and fell 32% from 2013 to 2014. The DS didn't start really declining to a major degree until 2010, thanks to the release of games like Pokemon Platinum, Dragon Quest 9, and Professor Layton, which lack proper 3DS successors. Smash Bros lacks the same punch. So if the NX was a 9th gen handheld system and came out latter in 2016, that would still give the 3DS a solid five and a half years plus time as a legacy platform. I'd prefer the 3DS last a bit longer, but am content with that timeline.
My main worry would be Nintendo's ability to get games ready by late 2016 and 2017. I can imagine a new 3D Super Mario being available for launch provided EAD Tokyo has been focusing on the NX since Captain Toad, but no other early hits seem likely. 2017 games may or may not include Mario Kart 9 and/or New Super Mario Bros 3 for the 2017 holidays, but NSMB3 might be delayed by Super Mario Maker. Pokemon Gen 7 could be released 3 or 4 years after X/Y, but would possibly come at the cost of Pokemon Z. That's not a bad early lineup, but this is a best case scenario IMO. Between the new hardware being developed and the surprising number of 3DS and Wii U games released from late 2013 through early 2016, supporting a new handheld might be hard.
But if it is the console or hybrid people have discussed, I'm skeptical. Nintendo has simply had too much trouble shifting to HD development to make an even more powerful console, and I don't think they've had enough time to make a hybrid platform since 2012.
