I'll challenge that. Seems to me interest in Wii had died long before Wii U was a concept. It sold as a toy, a fun thing, with little longevity. Sales declined YOY after the first year or two on the market, where every other console grows until the next-gen. And taking one of the many images with data from the web...By and large they failed to get the Wii customers to migrate, and a significant part of the blame lies on the decision to include the tablet controller as opposed to refined motion controls.
Look where Wii software barely registers despite its explosive beginnings (fastest selling console ever in the UK). It's a tiny fraction of XB360 + PS3, both in 2013 and 2014. Wii owners had moved on, and HD Wii wouldn't have faired much better in the long term. There's no reason to think that Wii HD would have seen the longevity and software sales of the other mainstream consoles. Charts and stats for earlier in the lifecycle are similar, with Wii collapsing quickly. It's the poster child for the fad, and fads are rarely repeatable as it's often their novelty that makes them so popular, which can never be repeated.