Well not just Wii U but also 3DS should have had some minor changes so I'll go over both.
3D was clearly a bad choice, it was an unwanted gimmick and inflated the price. On top of that it had a terrible post-launch drought so this is what I would have done.
Name-Super DS
Date-June 2011
Price-$169.99
Major launch games would still be Nintendogs+Cats, Street Fighter 4 & Professor Layton but pushing the launch back a few months allows for Ocarina of Time to become a launch title and round out the lineup.
Post-launch lineup
July-Pilotwings Resort
August-Steel Diver
September-Star Fox 64
October-Pokemon Rumble Blast
November-Super Mario 3D Land
December-Monster Hunter 3G (Japan)
None of the summer-fall titles are major hits but they would be enough to keep momentum steady until Mario in the holidays. Mario Kart 7 was rushed to make holiday 2011 but with a more straight forward name, lower price and no drought it would instead release in spring 2012 to give it extra time and give 2012 another big game to help momentum.
With steady sales the XL would release a bit later as well, in March 2013 alongside Luigi's Mansion 2 at $169.99 while the original model dropped to $139.99
Since there is no 3D, there is no need for a 2DS and the next revisions would be Super DSi & Super DSi XL in early 2015 at the same price as the older models, which get phased out.
Overall sales wouldnt be massively different but with better software pacing, price and name we see momentum stay more consistent than 3DS had which had droughts in 2011/2012 and constantly needed revisions to keep interest up.
Lifetime sales-~90 million
Now on to Wii U, many of the same things apply like changing the name, launch date, price and dropping the unnecessary gimmick.
Name-Super Wii
Date-November 2011
Price-$249.99
Hardware would remain basically the same but instead of the Gamepad they would go with improved Wii Remotes that have all the standard inputs like the Joy-Cons do. This allows them to launch at a lower price.
One other big change I would do is release it one year earlier. Nintendo tried pushing the fact that it could run PS3/360 ports but releasing when PS4/XBO were right around the corner was too little, too late and the extra year could have given 3rd party games a bit more chance to succeed.
Launch titles would be Skyward Sword as a cross-gen title and Wii Play: Motion would have been pushed back as a SWii title that came bundled with a pair of controllers. 3rd party aunch window titles would be Skylanders, Just Dance, Modern Warfare 3, Assassins Creed, Resident Evil 4 HD, Madden, FIFA, NBA, Sonic Generations, Mortal Kombat, Mario & Sonic Olympics, Rayman Origins, NFS: The Run, Arkham City.
2012 1st/2nd party releases would mostly be late Wii titles that switched to SWii late in development. Project Rainfall titles would be justified for releasing so late in the west because of this.
2012 lineup
Feb-Kirby Return to Dreamland
March-Mario Party 9
April-Xenoblade Chronicles
June-Rhythm Heaven Fever
Aug-The Last Story
September-PokePark 2
Oct-Zombie (ZombiU)
Oct-Nintendo Land
Nov-Super Mario Maker (team does this instead of NSMBU and becomes a big system seller)
2013 lineup would mostly be the same but spread out a bit more evenly with Rayman Legends remaining a Q1 exclusive and Pandora's Tower coming to Swii instead of Wii in the west.
2013 lineup
Feb-Rayman Legends
March-Lego City Undercover
April-Pandora's Tower
June-Game & Wario
July-Pikmin 3
August-Wonderful 101
Sept-Wind Waker HD
Oct-Wii Party 2
Nov-Super Mario 3D Land
Dec-Wii Fit 3
2014 onward would be pretty much remain the same with a price cut to $199.99 in May alongside Mario Kart 8. Since Mario Maker already released in 2012, we would see a traditional 2D Mario release in its place in 2015. 3rd party sales still wouldnt be great but better than Wii U and enough for some to continue giving moderate support beyond just the first year.
Overall sales still wouldn't be great but would be a big improvement over Wii U, perhaps 35 million.
Super DS+Super Wii (~125 million) would be a moderate improvement over 3DS+Wii U (~90 million) but still a huge drop compared to DS+Wii (~255 million) and simultaneous HD development between DS 3 & Wii 3 would be nearly impossible so Nintendo would still go with Switch as is in 2017.
When the herd loses its way, the shepard must kill the bull that leads them astray.
