To me it's not a matter of if, it's when. The Korean ratings board has an entry for, get ready for it, Fortnite on the Nintendo Switch.
Fortnite on the switch would be pretty huge. Arguably the most popular Battle Royale game right now, I'm sure there would be a huge audience for those wanting to play it on the go.
There's also an easily fake-able image of Nintendo's E3 booth layout that lists Fortnite there as well. For me, I'd put more credence in an entry in the Korean ratings board than the image, but we shall see in less then 10 days.