The problem with Nintendo is that they have a whole lot of really complicated problems, these problems all hurt Nintendo collectively. For example:
Terrible third party relationships is a major problem, and I would argue the biggest problem Nintendo has. Well how do they fix this? They would need to do a WHOLE lot to fix this. First of all, they would need to release a console comparably power wise to it's competitors. That wouldn't do it alone though, because they would need to build an install base that wants third party games. It's kind of a catch 22. They can't do it without third parties, but they can't really get third parties easily.
If I were Nintendo, I would start trying to become self sufficient. They really really need to stop the droughts, and if they are going to do that they will need way more first party. Right now it's embarrassing how poorly they are doing supporting two platforms at once.
Then I would try to make a decent, if not stellar online infrastructure. Accounts need to be there, etc. Just basic stuff definitely needs to be in place.
I would then make a console that had an updated G-Cube controller, and solid specs for as cheap as I can. Nintendo needs to embrace that they will be a second console, and make their console accordingly. If the Wii U had ditched the gamepad, slightly upped the specs, and sold for 250 at launch, it would essentially be embracing the strategy I am talking about.