Honestly, even leaving aside the fact that a Smash Bros film universe would be an extraordinarily bad idea from the start, the funniest thing is easily the extent some people think it would go.
Like there are some people that think it will not only include every Nintendo franchise on the roster, and even Nintendo franchises that aren't yet on Smash's roster, but all of the third parties as well.
If for some reason a Smash cinematic universe happened, let's be real. There wouldn't be third parties to muddy the rights even further, especially considering many of them already have their film rights with specific studios and companies. And going off of that? We also 99% wouldn't have Pokémon. The way the rights for that franchise work is well beyond the scope of something like this, in addition to the issues a lot of the third parties have.
And you would almost certainly NOT be getting movies for games that aren't even on the roster yet. Nintendo's a soulless megacorp. They'd absolutely go with larger name franchises that are still active over dead ones, and that goes double for dead franchises that don't even have a character in Smash. As much as I'd love movies for games like Hotel Dusk or The Mysterious Murasame Castle...it's not gonna happen lol. Let's be real here. They're not going for the title of Biggest Box Office Bomb by releasing a Chibi-Robo trilogy.
Even if this universe somehow got made, anything beyond the greater Mario universe, The Legend of Zelda, Metroid, Pikmin, Animal Crossing, and Splatoon, with Kirby, Fire Emblem, and Xenoblade being a step lower but still very well possible just due to their splits in ownership not being nearly as bad as Pokémon.
Beyond this, the only things I could see maybe getting in are Punch-Out!! (since it's already established as canon in the Mario movie anyway and could bank on the specific western nostalgia for it), Star Fox (if only because Miyamoto seems committed to doing things with it...it just depends on the extent), and F-Zero (and by this I mean Captain Falcon just appearing in the Smash movie... we're not getting F-Zero films). Anything else would be wildly surprising unless someone really wants to make an ARMS movie or something.
And honestly even all of that seems wildly optimistic about the extent it would go. It really does feel like people are enamored more by the idea of a Nintendo Cinematic Universe than they are about the logistics of how it would actually function. Like...this post only went into the "would the films even be made" angle, and not even any of the story or tonal issues that are alarmingly present.