I think fighter z for switch being announced is one of the likeliest announcements at E3 this year. Much like Fortnite.
It's not an overly amazing list of games but Fortnite definitely is good. Nintendo requires online pass for f2p games like Microsoft?
Yeah, it wouldn't be surprising. But good for the game. It already sold well, but can sell even better.
The only other fighting game on Switch that I'm aware of (aside from old 16/32-bit ports) is ARMS.
As for online play for f2p games, apparently you don't need a PS Plus subscription to play Fortnite with friends on PS4, but you do on Xbox One: https://metro.co.uk/2018/04/10/need-ps-plus-xbox-live-gold-play-fortnite-7455044/
So I guess it's up to Nintendo.