Exactly! I guess the SNES characters do fit that to a certain degree too (which is also why I support Doomguy).
Another crossover I like seeing is retro characters and recent characters. Look at Duck Hunt, Ice Climbers, and Mr. Game & Watch and then look at characters like Bayonetta and Joker. Not just the characters but also their games. Just never would have thought that they would all be in the same game together. It just didn't even seem likely. Heck, even characters like Cloud, with his reputation as a PlayStation icon, didn't seem like he could possibly appear with NES retro characters like Duck Hunt and Ice Climbers. I know Cloud is not really a recent character but you can't help but look the games they come from. Duck Hunt and Final Fantasy VII? Characters from those games together? That's still kind of hard to believe.
If we're going by NES icons, Ryu is the only 3rd party character from the NES era that I feel is missing. Him mixing it up with Mario, Link, Pit, Samus, Simon and Mega Man would be awesome for the hardcore NES fanbase (even if I'm not personally into the NES era of games)
Other crossovers I'm a fan of that I only recently thought of include the following:
-Joker and Byleth, because Persona 5 and Fire Emblem: Three Houses feel like similar games in a lot of ways and their sidekicks (Morgana and Sothis) share the same English voice actress. Both games are fantastic as well!
-Donkey Kong, Diddy Kong, King K. Rool and Banjo & Kazooie being together in Smash Ultimate brings back sweet memories of my Rare days during the 90s and 2000.
-Ryu and Ken, Kazuya, Terry, and Akira, even though he's an Assist Trophy, all being in one game is incredible considering they each come from a highly influential fighting game: Street Fighter, Tekken, King of Fighters and Virtua Fighter respectively. Also, Ryu and Ken vs Terry is likely the closest we'll get to seeing Capcom vs SNK 3, while Ryu vs Kazuya is the closest we'll get to Tekken x Street Fighter.
-Seeing Cloud, Banjo & Kazooie and Sephiroth in this game is still surreal to me, even if Banjo-Kazooie and Final Fantasy VII don't have anything to do with each other. I just wanted to point this out honestly.
-Cloud, Sephiroth, Kazuya and Snake make Smash Ultimate feel more like Playstation All-Stars than Playstation All-Stars did, even though THAT game had Kratos, Parappa, Jak & Daxter, Sly Cooper, Nathan Drake, Cole McGrath, Kat, Ratchet & Clank and Sweet Tooth all in it... and if Crash somehow winds up being the final character? That'll just be the final nail in that game's poor coffin.
-Sonic, Mega Man and Pac-Man being the mascots of Sega, Capcom and Namco respectively, and being together in Smash 4 and Ultimate, gives me Project X Zone vibes.