My 2 cents is that Smash has always been about video games first and foremost.
Other fighting games have always had a habit of throwing in other things that clashes with their ideals(Movie Slashers in the Mortal Kombat world honestly makes 0 sense), but Smash has always been consistent in keep things pure.
The most 'out there' we've ever gone is Cloud, who's primarily a Playstation character, and I'd be fine with an XBox/PC character truth be told, but I honestly feel like Smash should stick to video games only.
It's a slippery slope if you throw in anime. Sure, you put Goku in this game, then people are gonna want Luffy, Naruto, Sasuke, Sailor Moon, Jotaro, Detective Conan, Spike, Lina Inverse, ****ing Idolmaster, Hatsune Miku, Haruhi, Shrek, Cory in the House, Ronald Mcdonald, Burger King, thot, etc etc etc
It's a slippery slope.