People who are anti "grandfathering" are just misguided because we've all seen how important legacy and consistency are to Sakurai. He doesn't change characters to avoid alienating players, and, with the exception of ICs technical issues on 3DS, has never cut a character who appeared in multiple titles before. This of course won't be possible due to Ultimate bringing everybody back, but I still think more games = more likely. It's obvious that these characters forge their own identities and take on a different role in Smash itself. Their lack of main series relevance basically doesn't matter to Smash at this point. Plus, characters like Jigglypuff and Sheik have had perfect attendance since their Smash debut. In fact I'd go as far as to say everyone who was in Brawl and also returned in base Smash 4 has almost no chances of being cut.
Also, while we're on the topic of Pokémon, I'm revising my roster because I wasn't super satisfied with it and the Gen 9 Mon I settled on was Spidops. I know it seems kinda random but its anatomy is really unique, we don't have a bug fighter in Smash and it'd be the first non-bipedal Pokémon in ages. A bit of a surprise pick, but going for a fully evolved starter each time seems redundant. I also like the idea of breaking another so called "fan rule" and throwing people's expectations off because all the Pokémon talk has gotten super boring.