Sometimes it makes me wonder how it'd be like today if Breath of the Wild (AKA Zelda U) released in 2015 like how Nintendo said it would. Would the score rating be lower? Would it boost Wii U sales and hold off the Nintendo Switch for another year? What would be the Switches main launch game without Breath of the Wild?  

What I think:

I believe it would drive Wii U sales ALOT more than Mario Kart 8 or Smash Bros ever did. I believe the Switch will be held off for another year or 2. I believe Breath of the Wild would recieve a remaster port on the Switch. I believe Super Mario Odyssey would be Nintendo Switch's launch title instead of Breath of the Wild. I believe the Breath of the Wild's score would be lower because Ninendo literally had nearly 2 years of polishing sooo they must've improved ALOT in those 2 years. There would be more Wii U games out such as Splatoon 2, Xenoblade 2 ect.... and that's about it...

What do yooou think?     

If the Wii U kept its release schedule in tact without cancelations, push backs, and got dlc support for the games it did get, jesus. I couldn't even imagine. And that's not mentioning new games, ect. Just what it was supposed to get the first three years.

It would barely do anything for the Wii U, that system was beyond redemption at that point and Zelda has never been as big as 3D Mario, Pokémon, Animal Crossing or Mario Kart.

Hmm... Well, pretty hard to tell. It would not have saved the Wii U at all, or change many of Nintendo's plans (look at E3 2015. Put Zelda in. That's it). I'd think the Switch would've released this holiday, rather than March. Wii U would've gotten a few more games (more spin-offs? Pikmin 4?). That's all that comes to mind. Oh, FE Warriors would release on Wii U and 3DS, no Switch version. Most of the Switch games releasing before 2017 holidays would be launch titles (Odyssey, MK8, Skyrim).

Wii U might get nearer to gamecube sales numbers by dec 2017.

It would definitely have better sales, but not by too much

But the question is, would the game be basically the same as it is now?

Ehhh.
Wii U would have sold better for sure, but not enough to be respectable or for Nintendo to care, which is why delayed all this time to put it on the Switch in the first place. It would've taken it from the 13.5 million number it is at now, to around 17-19 million at best, assuming the 4 million people who bought Skyward Sword were holding off on the Wii U, specifically until Breath of the Wild came out in 2015. And even then, that's STILL worse than the GameCube.
I still think we'd be getting the Switch this year, but not until the holiday season as opposed to March 3rd, and I do agree that Super Mario Odyssey would've been its launch title.
I still think that games like Xenoblade Chronicles 2, Splatoon 2, and Fire Emblem Warriors would still be going to Switch, but they wouldn't arrive until 2018. This year, instead of the new Switch titles we're getting, the 3DS would be a much bigger focus. Instead of Mario Kart 8 Deluxe, we'd be getting a Splatoon pack as the 3rd Mario Kart DLC pack for the original version on Wii U, meanwhile Nintendo is hard at work with Mario Kart 9.
And that's just about all I can think of at the moment.

I think it was too long of a wait [for Zelda], but it's a good move on Nitnendo's part to release it for the launch of the Switch. The Wii U didn't create much buzz, so even if it's releasing on the Wii U at the same time, people don't care about that console and will see it as more of a good incentive to get the [fresh and new] Switch console.