Nintendo’s president Tatsumi Kimishima, in an interview with Time, has coyly addressed backwards compatibility for the Nintendo Switch, and by that I mean he pretty much avoided the question entirely.
The Nintendo Switch is an entirely new system, there’s no doubt about that. It’s a handheld / home console hybrid which takes cartridges not unlike the PS Vita. That means games on the Wii U which are in disc format, are not compatible. However that doesn’t mean they’ll always be that way.
Speaking with time, Kimishima answered the following as to whether the Switch would be backwards compatible, or whether they’d have to be re-released / remastered games like Mario Kart 8 Deluxe:
“We can take games and bring them and make them playable on Switch. So they can be remade for Switch, yes.
“That said, Switch is not backward compatible with games designed for other systems, and is not currently compatible with controllers designed for other systems. Support for certain controllers may be considered for a future update. In some cases, games from past systems may be re-released for the Nintendo Switch system as either enhanced or original versions.”
Mario Kart 8 Deluxe is essentially the same Mario Kart 8 which launched in 2014 for the Wii U however it comes with a number of new characters, new items, and a revamped battle mode. So, with what Kimishima said above we can likely expect “Deluxe” ports of some of the Wii U’s more popular games coming in the future.
Until then I wouldn’t ditch the Wii U just yet.