This is what I think would alleviate Nintendo's woes in the short-term, and increase the Wii U install base enough that there is a solid base to release large volumes of software and accessories on. Purely from a business standpoint, and not from "This is what I want to play right now as a gamer":
1) Drop price immediately to $249, and have two 32GB SKUs - one with NSMBU, and one with Nintendo Land. Include a Pro controller in each SKU, so every new Wii U owner has a GamePad and a Pro controller out of the box.
2) As soon as Mario Kart 8 launches, and some momentum is restored, and the sales trajectory is noticeably improving, release a "Nintendo Selects" line of Wii U software. Drop Pikmin, NSMBU, Wario, Wii Party, Sonic LW and 3D World all to $29.99. This will immediately increase software sales, and Nintendo can still make at least some money from them. Maybe 3D World could be $39 or $49 instead of $59, if $29 seems low. Whatever. The immediate goal is to increase software sales and generate as much interest as possible for the Wii U. This will have the added benefit of helping to bring back third-parties who have been burned by low Wii U sales ever since launch.
3) Completely overhaul the Wii U Virtual Console. Add the major NES and SNES games that are still missing, and add N64 games to the roster. Have straight N64 ports, and then offer premium N64 games for $19 or $29 each that have enhanced textures and character models, similar to WWHD, but perhaps not quite as much of a production. Make a big splash with the digital offerings. Go absolutely nuts. Make people say "Alright, I really need to go onto the eShop and check some of this stuff out. Nintendo's got a lot of good stuff on there."
4) All the while, as #1, 2, and 3 are happening, begin re-designing the Wii U and the nature of it's connection with the GamePad. Make the GamePad smaller, less expensive, and keep the screen the same size. Make it optional, instead of forcing you to have it turned on when you're playing with the Pro Controller. Make it more a tablet, and less a huge, heavy, bulky controller. Keep the buttons and sticks, but toss the giant plastic molding. It's been over two years since that thing was finalized, it can be done. Battery life needs to be doubled, while they're at it.
5) Allow the 3DS to be used as a Wii U input device. Design a way for the 3DS to output video to the Wii U, that lets you use your 3DS to play games on your television, through the Wii U. A.K.A = The natural evolution of GameCube's GameBoy Player, for a new generation of handheld and console. Allow for the GamePad to act as a 3DS while the 3DS is outputting to the Wii U, so you can use the GamePad to play 3DS games on your TV.
And allow the 3DS to be a controller for Wii U titles that don't require dual analog. If there are any. Basically, give players as much freedom and choice as you can. As I said earlier, go nuts. Don't hold back. No reason Smash Bros for Wii U can't be played with a 3DS connected to the Wii U. As an optional controller.
6) The pace of software released needs to be managed better. 3D World couldn't carry Wii U by itself through November and December. 3D World coupled with DKC Tropical Freeze may well have been enough to tip the scales and create much stronger momentum. We'll never know. That's in the past. What I'm saying is, big titles need to be released closer together, and at that point, momentum grows and the system takes off. But releasing one game every 3 or 4 months results in the system bottoming out before the next release, and then you're just clawing back instead of building momentum. Iwata is right about one thing: Momentum is extremely important in the console market. The problem is, having the software ready to make it happen.
7) Assuming all of the above has helped the Wii U to recover and it's managing 8-10 million units per year instead of 2.8, it is time to announce the successor you've been working on since 2013. No idea what it could or should be, but obviously it can't be more than $299, and it needs to have strong launch software ready to go day one. If the software isn't ready, then don't release the system until it is. In other words, do the exact opposite of what you did with the 3DS and Wii U launch.