I think I'm probably the first person here who would rather the crossover gets bigger than arming any given series with more characters. I've gone back and forth on what constitutes representation in proper, but at least for now I think that all representation is representation, and that while being a Fighter is technically a bigger honor since you will see use 24/7 all of the time, the fact is that once a series has one, it still has the one at least. So other characters getting "lesser" representation (Assists, Spirits, Trophies, Stickers, possibly Bosses, or even Stage elements on occasion) is still representation. Meanwhile, any series that isn't in at all is straight up nonexistent. Metal Gear completely imploded out of Smash 4, while to give a current example right now, it's as if Crash Bandicoot, Digimon, Tomb Raider or Devil May Cry never existed as far as Smash is concerned.
I want that number to go down. I'd prefer them to be Fighters as well, especially titans like the games I mentioned, but many other games like Puyo Puyo/Madou Monogatari, Undertale, Scribblenauts, Ace Attorney, Yakuza, Kingdom Hearts, Halo, Minecraft, and many, many more would have ludicrous amounts of people clamouring for them to join.
I have only been mentioning third-parties so far since, as I consider all representation representation, basically every first-party series worth mentioning is in (also why I didn't mention Shovel Knight, Shantae, Rayman, Tales, Tekken, and Monster Hunter). Still, many want to see Golden Sun, Panel de Pon, Nintendo Wars, Sin & Punishment, and several more Nintendo series join the fight.
Conversely. Many people would love to see a non-Sakurai (Bandana Dee I think counts as non-Sakurai, at least in spirit) Kirby character, or a non-Triforce Zelda character, or a non-sword Fire Emblem character, or Yoshi and Falcon to not be all alone. And I get that. I want a third version of Mario (one who would play absolutely nothing like him, but is still technically a Mario variant, think Samus/Zamus). But I think expanding the crossover is overall the better way, because that's a smile, a sign of love to people who will now be interested. It's a shout-out to passages of gaming history. And for my inner capitalist (read: if I were to remove the emotional aspect and rely solely on the financial one), it'll get people who are fans of those series to purchase (potentially) Nintendo consoles and (definitely) Smash copies, possibly including DLC, just to see a model with a bunch of data hit another one.
Assuming the repped series newcomers get the works (a stage, spirits, and possibly Assists/items, plus a good selection of music) then I'd be somewhat let down that they put that effort into a series with characters, over a series without. If they don't get that much content, then I'd probably be fine with it considering that a new series not getting that would be kinda lame.