No, I mean the Wii.  The Wii U was so bad of a failure that there is not a lot to learn from it other than to not be remotely like it ever again.  There was a lot to learn from the Wii though.

The Wii was a success, but it was short lived.  That is the main problem with the Wii.  It wasn't a sustainable business model for Nintendo.  Their developers didn't want to keep making "Wii style" games like Wii Sports and Wii Fit.  These franchises were hugely successful, but Nintendo doesn't make these games anymore.  They just didn't want to make them.  On the other hand the idea of having cheaper hardware and "different from the norm style" games was really working for them.  

The solution to all of this is the Switch.  It basically is a super-powered handheld device.  Nintendo has had a handheld business model for decades, so it is something they are really comfortable with.  With the Switch, Nintendo can still have a home console that is cheaper than other home consoles, but they make games that they are comfortable making.  It is both a really successful model and it is sustainable for them.  

The Switch is the sort of console that Nintendo could keep making forever if Iwata were still the CEO.  However, now that Furukawa is the President it is hard to say what direction the company will head.  I don't think we will have a good idea until the next Nintendo system releases.

Sorry to nitpick, but the bolded statement isn't accurate. The Wii was long-lived as far as Nintendo home consoles go. In Japan it is only topped by the NES and SNES, in the Americas it is only rivalled by the NES and SNES, and in Europe the Wii enjoys a very distant lead over all other Nintendo home consoles.

Here are some charts: https://www.neogaf.com/threads/nintendo-historical-shipment-data-1983-present.701305/

In Japan, Wii sold 1 million+ for 5 years - that's more than Gamecube, N64, and Wii U combined (4 years between all three), and not far behind SNES (6 years) and NES (7 years)

In the Americas the NES sold over 1 million for 7 years, and this is topped by SNES which sold 1M+ for 8 years. But this was topped by the Wii which sold over 2 million for 7 years in the Americas (data ends after 2013), and by comparison, the NES sold over 2M for 5 years, and the SNES for only 4 years.

In Europe, the Wii is the only Nintendo home console to sell more than 1M for more than 3 years, and not only did the Wii surpass 3 years, but it more than doubled it at 7 years.

But you are right about handheld success, Nintendo handhelds are vastly superior to home consoles in terms of longevity.

In terms of software, the Wii sold over 25 million units per year, for 8 years, and continues to sell in the millions per year to present day (interesting enough, the Wii U only outsold the Wii in terms of software for 4 years between 2015 and 2018, but Wii surpassed it again in FY 2019).