There is no question that the Wii U was grossly underwhelming as a console, it sold poorly, most people thought at first that it was just a Wii accessory that they didn't want to spend the massive money on, and third party developers very quickly gave up on supporting it in favour of Xbox, PlayStation and PC audiences. So in that regard it is, and always will be, a flop; however, not all flops go on to be remembered as such, some become future classics (Virtual Boy, Sega Saturn, for examples). Is the Wii U one of those consoles that, in your opinion, has enough going right for it to become a future classic?
For me, personally, I feel it has the goods to be a future classic. It has so many amazing first party games available (and yes, most of those are now on the Switch), it was a fun console to play, the gamepad was a great tool that was quite innovative for its' time, and there can be no doubt that it's sold poorly enough that, in another 10 or 15 years, numbers will be low enough that it will be considered somewhat rare. So, I'm going on a limb and calling it a future classic!