Unless any of us work for Nintendo, none of us are in a place to decide what's a difficult or easy job for them to do. Them saying they're very busy working on BOTW is a very broad term & can mean that they're on any development stage.
As of now, Nintendo haven't given any kind of release date...
All I'm going to say on the subject, @VitaTempusN92 is that not everyone can afford a Switch, and so they'll be more likely to get a pre owned or refurbished Wii U, which will still likely be sold for at least a couple of years still. Frame drops will happen in a lot of games, and I guarantee...