Right at the end of the latest Nintendo Direct had a surprising reveal. Super Smash Bros. will heading to the Switch sometime in 2018. Nintendo also showed a trailer during Direct:
There is no word on whether this is a new version of Super Smash Bros. from the Wii U, or a brand new title in the series. If ported from the Wii U, it could take the route of Mario Kart 8, arriving on the Switch with more content in a deluxe version.
You can see the rest of Nintendo Direct, here.