We cant know that yet.

How exactly you realize this in mid 2013. just around half a year after Wii U launch when in 2013. we had huge number of announced Nintendo games, just look that famous Nintendo Direct from January.

This became obvious at E3 this year.

Duh... Nintendo never really care much about WIIU. lets face this people.

They aren't that dunb to replace both at the same time. That would be economic nonsense. Deal with it. 3DS is going to be replaced next year and we have probably seen every Nintendo game for it.
Wii U successor will launch in 2017 and we'll get a ton of unannounced Wii U games until then.

That's almost fact.

No its not almost fact, all points that both 3DS and Wii U will be released next year, basically nothing points that this will not happen, and thats a fact.

My initial thoughts in the summer of 2012 after the Wii U had been fully revealed with features was that this could go really badly and I imagined it lacking basic appeal due to its attempt at aiming at all markets at once, this is usually a terrible strategy.
It had a decent launch window but then dropped like a stone after new year's and sold way less than anyone had ever expected, I realized that my suspicions were not only likely true; it was a lot worse than I had thought and from that point on I simply assumed that Nintendo would wake up to the same realization and never truly make an effort with the thing.
No amount of software would help it, the numbers were just so insanely low, there was nothing in recent times to compare it to in home consoles.

E3 this year? No, no, way before that. This has been obvious for quite some time now, especially with Reggie's frantic "the games are coming, hold on!" shouting and his insistence that every year will be "the year of the Wii U", and then nothing happens.
If it took this long to face the facts, people simply haven't been paying attention.

For reference, here's what I had to say about the Wii U roughly half-a year before it was released:

http://gamrconnect.vgchartz.com/post.php?id=4619667

I'd say that's a fairly good assessment of the way things turned out.

I don't care for what you see pointing to a 2016 release.

You should know that Nintendo isn't a dumb company. A 2017 release for the Wii U successor is the smartest thing they can do. And if you would be smart then you would realize that it is absolutely dumb to release both the Wii U successor and the 3DS successor in the same year. Just think about it. They would have to promote both, to get people buying both and to make launch titles for both simultaneously. Nintendo hasn't the capacities to do that. That's why the 3DS sucdessor is coming first and the Wii U successor is coming after that.

Um how could anyone possibly think Nintendo wasn't giving real effort during the same year Pokemon X/Y, DKCTF, MK8, Smash4, 3D World, Xenoblade X among others were all revealed?

Actually, I think it would be the other way around. First thing to arrive is MyNintendo and mobile games. Then, the NX home console. If the NX trully is a fusion device, the handheld part will need as much power as it can get, to work well with HC software. So one year more to improve the hardware of the handheld might help to close the gap. Also, the system that needs an inmediat successor is the WiiU, the 3DS is still doing great. It's baseline is usually between 80k-110k per week, those numbers aren't low enough to need replacement.

See my response above; with the first CY's sales numbers, I didn't think they would make much of an effort throughout the gen. They made most of their money on handheld gaming anyway.