Still don't really know how next smash can have a bunch of new and exciting newcomers without dipping a lot into third parties.
Personally, all the newcomers I care for are no-hopers at this point. (sorry wonder red and Viridi, you were no-hopers back then too)
So at this point . .i'm just hoping there are fun system changes so the gameplay is more fun . ..and enough of my vets i like manage to stay. If Sora finally gets added to smash and gets cut next game so I never get to play him i will RIOT
I think there are a good amount of first party picks left, especially if they open themselves up to not *just* going for the hot new thing.
But even if you're looking at just the Switch era and evergreen stuff, you still have the likes of Waluigi, Dixie Kong, Funky Kong, one of the Champions, Sidon, Raven Beak, Bandana Dee, Magolor, any of the Scarlet and Violet Pokémon like Ogerpon or Tinkaton or Gholdengo, Lyn, Edelgard, Dimitri, Claude, Oatchi, Tom Nook, K.K. Slider, Mio, Noah, Marina, Pearl, Callie, Marie, Spring Man, Twintelle, Ayumi Tachibana, Dr. Lobe, Ashley Robins, Snip and Clip, Officer Howard, and Ring Fit Trainee.
You could pretty easily craft a newcomer roster with some of those. Throw in a token retro character like Takamaru or Mach Rider or Sukapon, and then maybe an additional throwback fan favorite a la K. Rool like Isaac or Midna, and you're golden as far as first parties go imo.