If WiiU was a success and the others a disaster instead, bad for the industry then. 3rd parties would be turning their eyes onto smartphones more since Nintendo doesn't care about them, and less AAA games for the other two.

You should want to be hitting 10 million annually. At minimum 7.5 million units. If that was hitting 10+ million, it would probably be getting more 3rd party support from Activision, Ubisoft and WB, and things would be very interesting.

There are two different questions here and people are answering one or the other. First, is "What if the WiiU was from Nintendo's side developed and marketed exactly the same way as today, but was a success?"

The second is "What if Nintendo had made the WiiU into a machine that had a chance of success on the market?"

If the WiiU as it is currently had like 18 million units under its belt, that would mean the gaming market is very different from how it is in reality. It would never happen. People would have to value different things about a product than they do now.

But if the WiiU was changed into a system with lots of success for Nintendo, that would be fantastic and I would enjoy it. There would have been third party games released all through this year! Marketing would have been different. The system itself might have been different.

I'd say as a sales benchmark, the level for WiiU to be considered a success on the modern market is LT at like 35 million evenly distributed throughout the generation. Because that's reasonable market presence to stay relevant in a consumer's mind all generation. But the real decider is profitability.

if the Wii U was a success I would own one. I kinda want it but I am afraid that it will be a "Dreamcast" purchase for me

Wii U wouldn't be a success, just because the Wii concept itself is outdated and unnecessary today -- in 2006 how many games were made expressly for casuals? Maybe like five? Today there are thousands, thanks to iOS/Android, and the problem of traditional controls has been solved by easy touchscreen controls.

So there is no need for the "Wii" ... today it's just an overly expensive concept with $50-$60 games that no one wants. The novelty of looking silly waving your arms around in front of the TV fizzled out a few years ago too. It's not a "wow, I need to have that in my life" thing anymore in gaming, people got their fill of Wii Sports, Kinect Sports, and bazillion other cheap mini-game knock offs the last few years that they're not interested in doing that again, just like guitar/music games got tired after a few years and having tons of plastic instrument junk laying around the living room.  

If you want to make games for the casuals you have to play by the new rules that Apple has set for that part of the market -- games must be dirt cheap or better yet free and stripped down of play mechanics to be very simple, and the hardware has to be a cool fashion statement ... things that Nintendo isn't able to deliver on.

iPhone is simply just a more appealling casual platform than the Wii ever was. 

If Nintendo had made a reasonably high powered console (something legitimately 3-4x more powerful than a 360 with about 4GB of RAM) and planned their software releases better, ditched the Wii brand, I think they'd be headed to a comfortable 2nd place finish this generation with a fairly profitable console that would sell about 40-60 million units.

MS made so many mistakes this gen with a 1 year head start, Nintendo could've capitalized.

Everyone  knows Wii U is a great console but OP is discussing  "what if ". So that's not part of discussion.

My response to OP is:  PS4 would have been failed miserably because every casula  prefer  less expensive console that utilize gimmick like Wii and Hardcore gamer would choose Xbox one  with their game console and cable box hybrid. But no metter what happen with Wii U, the tablet industry is still there and will still halt the succes of Wii U. So the succes of Wii U have some correlations with the succes of Tablet and Smart Phone  in the gaming market.

I knew from when they first showed the Wii U at E3 in 2011, that this console will flop.

It would be another Wii.

Would be filled with shovelware like Dora the explorer and barbies dreamhouse studio
and then third parties would moan nobody buys their games and would stop developing for the console.