You can try inserting Wii U discs into the Switch. Let us know how that works out.
The trailer pretty clearly showed Nintendo's plan is to resell Mario Kart 8/Splatoon on the NS anyways as "remixed" editions anyway. There's clearly new content/changes in the Mario Kart and Splatoon clips from the NS trailer.
Those games had their sales potential cut off by poor Wii U sales, now Nintendo is going to recoup their oppurtunity costs on those games by charging you $50-$60 for them (again) as well as getting money from those 3DS owners (80% of them) who didn't own a Wii U.