How do you propose to port a game that isnt finished yet. It takes a year of development to port a game.

This is exactly the problem i have with these theories. You think this is all easy and trivial to do. Games development takes a long time. Bringing out a system require alot of resources. This isnt done over night. Retro is the only studio i can see would have enough development time to come up with something. But if you think that NX development kits cant have been ready any earlier than in the last couple of months, you are sugesting again the development of a game in 1 year.

Because as I just explained, while they always work on their next console right away, they never publically announce it until they're getting ready to leave the other console behind. That's why Sony kept denying that they were inquiring about PS4, when that was in fact exactly what they were doing.
Doing and saying are two very different things. How many times have we not heard game companies claim "we currently have no plans regarding that" or "we have nothing to announce" about something, and then just weeks later, they make an official announcement about it? Because there's a proper time for announcements.
Talking about your next console only has negative consequences for the sales of your current console, which isn't worth it unless you see more gain in getting people thinking about your next console. This includes developers as well as gamers. For example, Square Enix said that they are considering putting Dragon Quest XI on NX. They would not say that for a game with a 2016 release date, if Nintendo, and every other company, announced their next consoles as soon as they start working on them, or several years before they come out. When they start publicly talking about their next console, that means it's coming sooner rather than later, as the company is willing to diminish sales of their current console (WiiU) just to get the word out. I already have friends saying they'll skip WiiU and wait to see if NX has backwards compatibility instead. Since Nintendo are clearly hoping for better software support for the NX, they potentially stand to gain from someone buying an NX, than a WiiU. Not only that, but early adopters are more likely to purchase more software than late adopters.
And if a Wii U owner for example considers buying another console because they're disappointed with the outlook for future games for the WiiU, he may change his mind and wait for the NX instead if he hears Nintendo talk about it and thinks it's not as far off as he initially though.
Likewise, if someone is thinking of buying a WiiU this year, they're less likely to also buy an NX if it launches this year. Which means less early adopters. Which can snowball into less support in general, and cause third parties to doubt the potential success of the NX.

Bottom line is, each company starts R&D immediately for the next console, but they never talk about it until it's close to reveal and release. That Nintendo did it after only having WiiU on the market for less than 2.5 years, is not a a good sign of a console that's going to last a normal console life cycle.

As for how I conclude when the next console is coming "from that", it wasn't just from that. That was only a part of it. I concluded it based on many different factors, which are present in the post I liked.
For someone who apllauds another user for "actually thinking", you're not exactly showing signs of being willing to do the proper research, as you didn't contest a single point I made in the post I linked, which is where every important detail is compiled. Do point out where my reasoning is wrong there. Because if it's not, then absolutely nothing points to WiiU lasting through 2017 with any meaningful support. More games like Amiibo Party are not going to cut it.

Xbox, a more successful console than WiiU, only lasted 4 years. WiiU, on track to be the least successful console in history between the big three companies, will be 4 years by the end of 2016.

So the 3DS, which sold a lot more than WiiU this year, needs a replacement first? You're gonna have to explain your logic there. In just the first 6 months of the year, 3DS sold more than twice as much as WiiU did for its first 9 months.
They're both running out of support, but one is still selling significantly better than the other. Also, the WiiU brand is something they'd want to disassociate themselves with as soon as possible. Which is probably why they made it clear that the NX won't be in the Wii family.
Also, as I mentioned before, GBA and GC launched 6 months appart.

As for the successor comment, Nintendo also said that the DS would not be a successor to GBA. And we all know how that turned out. It had two screens, and a touch screen. But for all intents and purposes, it was.
If NX is not in the Wii family or the DS family, then that could be one way of putting it. But either way, a new console is coming. And a new console will be considered by everyone as a replacement for the WiiU, no matter what Nintendo call it.
You also have to consider that they'd be unlikely to want to associate themselves with the Wii brand any more, so saying that a successor to the WiiU is coming could be misconstrued, and they'd have to go into more detail to explain how it's not related to the Wii family. Details they don't want to talk about right now. So saying that it's not a successor, just like saying that DS is not a successor to the GBA, is a simpler and more convenient way of putting it.

It's not impossible to have a launch lineup ready at all. When was the last time Nintendo started development for any quality game? The last time they announced any new quality project for WiiU was back in mid 2014. So that would be grouped together with Splatoon, Mario Maker, Star Fox and Zelda.
Every announcement that started development since then has been of the quality of Amiibo Festival and Mario Tennis. A WiiU port of Pokken was very likely part of the original agreement back in mid 2013, in return for letting Namco use their popular IP in the arcades. And the Zelda TP port started development several years ago.
So by this you can conclude one thing. Somewhere during 2014 Nintendo moved all new meaningful development resources over to NX. At least when it comes to new games. Because we haven't seen a single announcement of that nature since. There was an article posted recently, where one of the developers of a noteworthy PS4 launch title, the name of which escapes me at the moment, said they recieved a PS4 dev kit just 6 months before PS4 launched. So having 2 or more years to develop launch titles is plenty of time. Especially if third parties are more interested this time around. Square Enix with Dragon Quest XI could be one of them.

A successor to the 3DS would get software from this automatically, and vice versa, if the shared library idea is true.
And of course, a company will always say that they are still dedicated to support their current console. DLC for current games asside, there's been no sign of meaningful support for the WiiU since mid 2014 in terms of new games. It's either rushed budget games like Amiibo Festival and Mario Tennis (which can be a good game, but this one lacked a ton of features that the previous one had), or games that were supposed to be released in 2015 but delayed until next year, or games that started development years ago (Zelda TP, Pokken) before Nintendo realised they had to move on from the WiiU sooner than expected.

Well, it seems that, out of the three big western publishers, Ubisoft is the one more willing to give Nintendo a chance. Activision stopped the support once they saw CoD couldn't sell, and EA outright boycotted the WiiU with that unnacceptable Origin deal. Ubisoft kept the support for a while, albeit with weaker versions of the games, and no DLC (but they are hardly the only ones).

Even if Ubisoft has less hopes on the NX, a vita port of a game four years old from a franchise that didn't sell well on Nintendo platforms to begin with seems foolish. A port of Grown Home would seem more plausible.