I was thinking about how Fortnite handles R-rated properties with the recent Peter Griffin announcement, and honestly I actually think "this is a kids' game" is a good argument FOR the likes of Grand Theft Auto, Mortal Kombat, Doom, or Call of Duty in Smash. They should still absolutely no-compromises no-loopholes be in a censored format, don't get me wrong, but when you're a kid, those 4 franchises are these alluring, mysterious things you crave just the slightest glimpse at - as a kid I was staunchly in the anti-graphic violence pro-platformer Nintendotuber sheep camp, and even I was a bit curious what the GTA fuss was - so having a family-friendly rendition in Smash would be a nice way to statisfy that hunger for the forbidden fruit without either compromising the actual source material or exposing kids to dead hookers, brains being sliced in half, and Ollie North cameos.
Maybe take a page out of Fortnite's book and have a universal stage hazard that forces two players closer to each other? Sorta like Ultimate's Sudden Death cam but much less extreme. It could close in at different set times during the match or whenever someone's been camping/playing neutral for too long.
In most cases I don't think it would work in FFA or Teams because you don't have an opportunity to camp or play long games of neutral. Except for big stages like Palutena's Temple, in that case a storm mechanic could make it actually fun.