Anything built by humans will degenerate and fail eventually.
Nobody has a magic crystal ball
that tells us how durable the (still young) Wii U is. Time will tell.
- One general issue I know is the Gamepad being always on (like @alexander1970 mentioned) repeatedly deep discharging the battery if not disconnected or charged regularly. It's bad but just an easy to replace battery.
- Another stupid decision (probably for DRM reasons -- what else?) is to have the motherboard and the drive board being married to each other. If the drive fails and you get another one you have to keep the old logic board and install it to the new drive. The Wii U will not boot up without the drive. But even if the laser fails there is no problem as long as the drive board is okay (backup your discs on time and use USB loading for both Wii and Wii U games)
- Wii and Wii U drives (slot-in) are prone to having shoved random garbage into them by small children. This can cause serious damage to both the drive and games. Tell children not to do such nonsense if they are old enough and keep toddlers away from the consoles.
Nintendo hardware has been very sturdy in the past (seems it changed with the Switch Joycons and the folding design of the DS systems causing mechanical stress on delicate ribbon cables -- but these things can be repaired and third-party replacement parts should be available for the next decades).
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About disc rot
If stored cool, dry and dark, pressed optical media will most likely last very long. The BD type (which Wii U games are similar to) has a very hard protective layer against scratches as well). Few of the first audio (CDDA) have had a problem with bad adhesive allowing some kind of fungus to get inside and destroy the data layer if I remember that correctly.
I have several hundred pressed discs, some of them are 30 years old. Audio CDs, video DVDs/BDs, PC games, Console games. In my collection two discs failed because of disc rot and they are from the same pressing... so I guess it was a manufacturing defect (Command and Conquer Red Alert 2, both disc have become white inside -- data still readable but the SafeDisc 2.x weak sectors copy protection does not accept them as genuine discs anymore).
Backup all your data nevertheless. You never know. When the time comes that Wii U consoles eventually all fail it should be possible to emulate the games near to perfect. Ironically the biggest issue to run old Nintendo games nowadays are the non-existing analogue inputs on modern TVs -- (S)NES and N64 are still working as if it was the 1990s. AV to HDMI/upscalers are fine -- if you find one not introducing lag.
Good luck and have fun!
