The 2016 Pokemon game will be on 3DS, as well as Pokken Fighters on Wii U. GameFreak has a history of not fully supporting Nintendo's consoles at launch.
Yeah, they're reusing assets. They have to because they're pushing games out so quickly. Did they make low-effort games like Captain Toad and TriForce Heroes so that they could work on other games at the same time, or so that they could finish those games extremely quickly? *shrug* Maybe both. Captain Toad was made in just a year though, surely it took a decent amount of attention to push it out that quickly.
You're being pretty generous to suggest that all of these teams could make a full game in under three years. You saw the trouble Nintendo had with Wii U games. You also forget that EAD 4 is hard at work on Mario Maker and EAD 5 is fully committed to Star Fox and Miyamoto's pet projects. Sure they're working with Platinum. Again, is it so that they can finish this game in an unreasonably short time or is it because they're simultaneously working on games for another system entirely?
As I mentioned before, why haven't we heard any rumblings about this system from third parties? The Wii U cat was already out of the bag by the time Nintendo officially unveiled it at E3 2011. Yet there isn't a whisper about their next system. Jokes aside about Nintendo not even bothering to send dev kits to third parties this time, somebody ought to have spilled the beans by now.
All of this is also assuming NX is either a home console or the mythical fusion machine. What if it's not? What if they also have a separate handheld on the way? How does that fit into this?
Anything is possible but my gut says they aren't ready for a 2016 launch.
I don't know about that Gamefreak Pokémon game. The next thing in line should have been Z (or an X 2 and Y 2) and ready for this holiday season. It seems like the usual pattern doesn't hold true anymore.
The next systems shouldn't be as much of a change for development as Wii to Wii U was, so getting to grips with new hardware won't be as big of an issue. I didn't mention the teams that are working on Super Mario Maker and Star Fox, did I? The other teams are certainly working on unannounced projects though.
It could simply be that nobody has been motivated enough to break an NDA yet. Besides, Nintendo themselves hinted at a few things, so what's the point in breaking an NDA to confirm it? Nintendo saying it is already confirmation.
Of course there's a handheld underway. Have you been living under a rock? Nintendo has merged their R&D for home consoles and handhelds because in the future their systems will be like brothers, similar to how iPhones and iPads run the same applications for the most part. So same OS for home console and handheld, plus games that will run on both devices. That's how Nintendo aims to combat the droughts that have plagued their previous systems. And if you think about that, it points towards a simultaneous launch for the next Nintendo home console and handheld, because the previous reason to stagger the launch of two different systems obviously doesn't exist anymore.