There is a Splatoon Discord but it's a little obscure since most of its members pretty much left VGC so no one comes here to share it in the first place
But if you wanna set up tournaments on VGC and all, I guess the NintenDominion thread is probably the best place to do it, as long as it is something you can host on the thread yourself, which I'm not sure will be the case. In any case, it can only be a good thing to have this kind of thing around, VGC is in dire need of some activity. People are leaving because they get bored of how stale the community's gotten, and with fewer people it only tends to get ever more stale around here, so it's nice to see someone trying to get things going because it's gonna start turning things around.
Personally, I think I'd be down. Mario Kart 8 would probably be a fun time since it's a more casual game where loads of people can play together with ease, so that would be cool. Splatoon 2 is a tougher one to host organized tournaments for, but I guess I'd enter occasionally if it worked. And Smash Ultimate is Smash Ultimate, of course, it's gonna be a great time always.