You have to keep in mind that even if NX (home console) is released in 2017... it would be launched just some months after 2016 ending. I mean, they can't wait until Spring/Autumn/Winter 2017 because they just don't have games to support Wii U that long.

So, I think is irrelevant in which year the consola is launch, because the difference of time will be three-four months AT MOST.

Take Two? Bethesda? Warner Brothers?

And when exactly do you suggest it should launch? Cause I see the PS4/XB1 going strong until 2019 or 2020, so to avoid competition they would need to hold on and support the Wii U for more 3 or 4 years? Yeah, that's really impossible/crazy.

I'll tell you something: the NX won't be a PS4², or else it would fail. It will probably be a moderately powerful console with some concept that's new and tries to get people's interest. If it's good, well marketed and has a good quantity of games... it will sell.

If they were to go up against the PS4 and One in 2017, would that make any difference? That would make it even worse since they would have an even stronger hold on the market by then, trying to wedge in a third wheel after four years is a ridiculous idea.

OP makes the same supposition that the NX will be a very direct competitor to the PS4 and One, I'm not so sure this will be the case, and thus the whole 2016 vs 2017 debate loses value if these are the parameters set for discussion.
In short; what the PS4 and One do is unlikely to have a huge impact on the NX since it is very unlikely to aim for the same exact audience. As for chasing proper 3rd party support; that ship has sailed nearly two decades ago, and Nintendo know this, that is why they've been talking about a unified structure in their software and hardware divisions, to lessen development time, budgets and have a bigger total offering on each individual platform in the end.

So you suggest to release the thing when the rival consoles install base is 70Mish instead of when it's 50Mish because everyone would say "All my friends own a PS4, so I'll buy one too" when the console has 50M install base ? don't you think the same could be applicated to 2017 and it would be even WORSE since the instal base is like 20M more ? Shure your argument is full of logic *irony*
AND do you realize that the last title released in the Metroid Prime series was on the Wii, right ? and not only that but we got even a collection with even the first two games along with that ?

The only reason to wait for 2017 over 2016 is for more Horsepower but honestly Nintendo couldn't care less, whatever other console comes from Sony/Microsoft next will launch in 4/5 years from now, it'll certainly be more powerful than the NX. with the current technology it's already possible to make a console that is way more powerful than PS4/X1(hardware from 2012) at almost the same price of those two consoles...
Also in 2017 both consoles will likely get another pricecut to 250 or maybe even 200$, that could be harder to top aiming for the same price if they want to do a more powerful console, even if they use 2016 tech...

Some may disagree with me but the only way to convince the mass amounts of people to get a Nintendo console would be first and formost to get the third party on board, people love Nintendo first party but aren't willing to buy the console due to lack of third party support. (especially those who can only afford to have one console) To the non hardcore Nintendo fan a console with Nintendo IP's along with a similar Japanese third party support as the PS4 + all the big western publishers - EA, Ubisoft, Activision, Bethesda, Warner Bros etc releasing there stuff on its platform would make more people actually consider Nintendo instead of disregarding them completely.

Also from Nintendo financial side of things getting the third party support = free money from platform royalties.

Agree mostly except the Wii thing. Having a gimmick doesn't equal another Wii, nor does it mean absence of core franchises. If they're launching in 2016, they have to be going for USP which would enable them to be a secondary console purchase. A handheld/Console hybrid where you have a portable around Wii U strength and then a docked device close to X1 power would achieve this. They'd have at least 50m users waiting to adopt simply for the handheld function and then another 15-30m for the home console depending on how much support it gets.

Alternatively they could simply be releasing a 9th gen system early to the market, so the system isn't just there to compete with PS4/X1, but there to replace them a few years down the road. In the meantime (2016/2017) hardcore Nintendo fans and core console gamers who care about specs/performance will provide the system with its early adopters. Problem with this logic is that it'd make much more sense to release a system designed to replace the PS4 in 2017, rather then 2016 but maybe Nintendo are going down a scalable hardware route, something one of their recent patents hinted at.

Again, explain me why it's better to try and replace a console with 70M userbase instead of one with 50M userbase...

Well it could just be a handheld, or if it's the fusion thingy the handheld could release in 2017 and the console in 2018

i find that statement ludicrous.  the competition there is even more greater.

+ the android, windows, and amazon based equivalents.  that is not an easy market to compete in.