Nintendo would never release their next gen console 4 years after the release of the last one, which is what you're suggesting if they release Nintendo Fusion or whatever it's going to be called at the end of 2016. As others have said New 3DS hasn't even launched in the west yet, a year and a few months shy of 2 years on the market was never going to be the lifespan of their most current handheld.
Most likely New 3DS was released to keep 3DS architecture on the market until it's time to launch this unified Handheld/Home console that has been rumored (assuming the rumors are true).
Another factor that disputes this assertion of a 2016 release is that some major Processor and Memory architectural changes will be occurring in 2016, which means that those developments need to filter down into manufacturing for costs to become reasonable to implement for the console market.
AMD will start to manufacture a new ARM CPU core (for the handheld) and they're also re-entering the multi-threaded CPU core market with their Zen line of processors.
There's also the advent of Universal Memory which will potentially go into production for the server market next year, but costs will be very high in the beginning, so a few years to reduce that would make all of this brand new technology much more affordable and that means Nintendo can still be the pioneers of all of this new tech in the home console and handheld markets.
By 2017-2018 cost of manufacturing will have come down.
Launching in 2016 is a mistake, makes no sense unless Nintendo wants to use archaic technology compared to what's going to be available to them a year or so later.
Another factor to consider is that Sony and Microsoft won't be launching until 2019 at the earliest, if Nintendo shares similar architecture to PS5 and XB2, as well as having comparable performance, which will be a huge improvement over PS4 and XB1 then they put themselves in a position to actually gain 3rd party support.
With fusion the handheld market may become a consideration to 3rd party publishers if porting to the handheld side is a none issue from a development point of view, because this unified API will just mean it's a part of building the Nintendo console version of those 3rd party games.
Nintendo may just hit the nail on it's head if they can wait and build Fusion as the first console platform to use Unified Memory, AMD Zen and their ARM K12 technology, along with the current GPU tech of the time.
Sony & Microsoft will use the technology a year later, so it makes sense for 3rd party to port across all platforms.
Nintendo would be fools to go with the older technology that would be available at production for launch in late 2016. 2016 makes no sense! Not from a launch schedule of past platforms point of view, on the handheld or home console markets and absolutely not when you look at the huge upgrades in technology that will potentially be available to any console platform holders a year later.
TBH keeping within a year of the launch schedules of Sony and Microsoft actually makes the most sense because it means costs will be that bit cheaper and Nintendo has always been about launching at an affordable price.
IMO 2018 would be the sweet spot for Nintendo, it gives Wii U 6 years on the market, New 3DS is seen as a slight evolution over 3DS, so 3 years on the market would be fine and then Nintendo launches with the new architecture to back the fusion home console.
All of these things just work so logically together, even if you take out the whole fusion handheld/home hybrid console aspect you still have the home console platform sharing similar architecture to what the next Sony and Microsoft platforms use and being different to the majority is what has caused the majority of issues with Nintendo getting support from 3rd party publishers.
A 2018 launch actually makes the most sense and it's Nintendo that actually needs to have the courage to compete, not Microsoft and especially not Sony that needs to worry about anything, especially when they can outsell Nintendo within a year of being on the market, when Nintendo has already had 2 years on them.
Nintendo needs to do whatever they can to get 3rd party support back, like it had in the SNES days.
