What if Nintendo Skipped the Gamecube?  What if the Wii was their sixth generation console, the Wii U was their seventh generation console, and something else was their eigth generation console?  Would the Wii still have sold 100M?  Would the Wii U have done much better than it currently is?  And then what about their eigth generation console?

Then Wind Waker wouldn't exist
And I would be sad

The wii would seem zomfg magical with that tech in that time so yea, it would have probably sold even more

I wouldn't be. I'm tired of that game and it's revisionist (GOAT) history. Back when it launched, people my age (21 and over) panned it. It was good, but that's it. The people who claim it's some mega godly, epic adventure are usually in their early to mid 20's, who are blinded my their own nostalgia. Good game, not great. 

As for the OP's question, I think Nintendo would have bombed had they released the Wii during the PS2 era. Back then, much like right now, core gamers ruled the industry. No one would have wanted to play a game like Wii Sports back in those days. Not enough violence, blood and mature content. That's the reason why Gamecube failed in the first place. PS2 had GTA. Xbox had Halo. Gamecube? Metroid Prime. I loved that game to death but bringing it up online was a death sentence. 

Wii would've been so advanced, it would've been the best selling console of all time, and Wii U would've actually sold well.

I thought it was common knowledge that we wouldn't have the Wii without the technology behind the Gamecube. So technically speaking, the Gamecube as a 6th generation device was already ignored by Nintendo.

If Wii came after 64... let's just say it would have sold a lot more than 100M. Technology that woked like that was still unheard of in gaming. It would have exploded even further. Who knows what kind of games we would have gotten for it...for better or for worse.

The PS2 had variety too, with a great number of -E- and -T- rated games being released on the system along with the M games.

Also, it's arguable that the original Xbox had similar mature content as the PS2 and sometimes more exclusive mature content with better online.  Though even that didn't help the Xbox sales-wise.  In the end the Xbox only sold ~2 Million more than the Gamecube and also lost by a great margin to the PS2.  

It would be revisionist to call the original Xbox a success when it's just as much a sales failure as the Gamecube, and a even greater failure financially.

Your forgetting the price though, it would be a lot more expensive than what the GCN was. Likely would have sold a lot worse than the Wii really did.

Same goes for the WiiU. I mean its overpriced now, imagine it in 2006.

If the Wii came out in the 6th generation it would have blown peoples minds! A console that small with that little power consumption that blows the allmighty Xbox out of the water technically? That would have been a friggin' miracle! It would have dominated so hard that Sony would have quit the console business. Microsoft would have bought Nintendo because they saw that they have obviously no chance to compete with Nintendo on a technical level.

So in this alternate Reality, the Wii U would have been the only console released in Gen 7. But it would be a Microsoft product so it would probably be called Xbox U. All your Marios and Zeldas are right there next to Halo and Sony is a 3rd party publisher, unless they sold all their developers.

Because of that monopoly and sales of 200+ million for a single console, Apple as the allmighty savior has to step in. They would have brought a console in Gen 8 to compete with Microtendo which on paper isn't that impressive. It has no chance by specs, but a shiny case out of metal! It's also available for as little as 1.999 $. And it will sell like nuts for some reason nobody on this planet understands...

Written with my MacBook Pro 13" Retina (Late 2014)