I'm with mZuzek on this one.
Exactly what they did. The only thing they should have changed was the name, call it Wii 2, or anything else. It wouldn't have done much to help sales, but anything would've been better than 'Wii U'... Though, now that I think about it, I don't even think I'd have changed that.
There's an old saying: Sometimes, you need to fall flat on your ass so you can get back up, learn, and do better. Basically, first you need to fail in order to succeed.
If Nintendo had been successful with the Wii U or whatever console they had from 2012-2016, they may not have seen the need for the Switch and we never would have gotten it. They'd probably still be making one handheld and one console, splitting their resources between two systems. We'd have a successor to the 3DS out already, with the Wii U's successor coming out this or next holiday season. They needed a Wii U disaster in order for them to see their mistakes, rethink their strategy, and take advantage of their unique strengths, and that's what has led to the Switch.
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