NSMB U seems like one of the Wii U games that does not need to be ported imo, just make a new 2D Mario at this point, but if it happens then whatever.
Even if 2018 for Switch does have a lot of Wii U ports there will still be plenty of new exclusives that are already known as well like:
Project Octopath Traveler
Metroid Prime 4
No More Heroes: Travis Strikes Again
Kirby Star Allies
Yoshi
Mario Tennis Aces
Fire Emblem
Runner 3
The Wii U ports don't take away anything from the existing lineup of new games, there's still plenty of new there as well. The Wii U ports make it better for people who never owned a Wii U but own a Switch now since, again, those might as well be new games to them.
Plus I still personally think there will be either Animal Crossing or Pokemon this year, if they can't get Pokemon out in 2018 i'm thinking they'll push Animal Crossing to that spot.