Wii U had so much potential but marketing and lack of games made it failure. I still love it and it has amazing games. I feel sad how it didn't get as big as Wii did. I remember many of my friends saying: '' I will get Wii U when new Zelda comes out''. And this was 2 years ago :D Hopefully NX and new Zelda will be succesful! I don't care so much about delay, I have plenty of games to play before it drops. Maybe someday NX will have Splatoon 2?
I think Nintendo, and in particular Iwata, learned the wrong lessons from the success of the Wii, something he slightly admitted to later on. I think he though the Wii was wildly successful because it proved gameplay is more important than graphics after all, and because he successfully tapped the untold millions of non-gamers into the gaming fold as he set out to do. It was only after the WiiU started tanking that he started to realize the "casual" gamers are fickle, move on and were NEVER really brought into the dedicated gaming fold, and that the Wii was successful for its faddishness, not because it was a beloved gaming system. The NX I presume is born out of that belated understanding.
However I also believe the WiiU was NEVER meant to be a long term console, the merging of handheld and home platforms was something they'd determined to be essential before the WiiU ever released, and the WiiU was only meant to be a short-term stop-gap to fill the HD hole while they reorganized the company to merge the handheld and console businesses. It had a limited library because they were never going to pour tons of resources into it. I think the failure was bigger than they expected and thus the library was even smaller than they expected. But WiiU always seemed like a holdover until everything game together. Remember they merged the handheld and home hardware divisions and broke ground for the merged HQ the month WiiU released. NX was already the overarching corporate strategy the day WiiU hit shelves. But I also think Zelda was SUPPOSED to be WiiU only and was pulled only because they expected it would do somewhat better than it did.
Keep in mind, though, that Splatoon didn't take off and start selling consoles until right around when Iwata died, and the company was almost entirely directionless for 6 months after that as Splatoon rose (thus the "we're done Splatoon updates, wait no we're not!" not being in sync with "hey this game actually sells!" I think company strategy was set in motion around last E3 when things were looking grim, and after Iwata died everyone stuck with his existing assumption the platform failed and kept progressing in that direction - nobody noticed until too far along that thanks to splatoon it started NOT failing as hard as it seemed.
I still love the WiiU - it's basically a console "just for the fans" from the start, so while it has very little, 100% of what it has is just for us. Except AC Amiibo Festival. That one isn't. :P