Am I the only one who could see both EarthBound boys being cut? The series isn't a mainstay, and while the original 8 is sacred, I don't think the same about the original 12.
I've spoken on this before but like... let's exempt Ness from the legacy points and Original 12 status for a second.
Mother still has a wealth of content in Smash. It has two characters, four stages, classic items in Mr. Saturn and Franklin Badge. Lots of beloved music, a couple Assist Trophies, you get the picture. Every Smash has made a deliberate attempt to retain content from the previous entries... if the entire Mother series was cut from the game, this loss would be catastrophic. Maybe this is just by circumstance - they've had over 20 years to build up this amount of content. But to clear the board on all of this would be absolutely jarring. I truly truly cannot see it happening even withholding my bias toward the series, unless Smash truly sees a full on, scorched earth reboot.
(And yeah I mean, you could bring back a lot of that stuff without Ness but... why?)
Ness is also an extremely popular fighter. While there isn't an official statistic I can point to outside of fan cultivated graphs, I can say with relative confidence that Ness sits among the most played characters in both Smash 4 and Ultimate through my own observation. Largely devoid of any meta influence, he just is a very common pick up and play character with presumably a base of players who are very dedicated to him. He's also arguably the first mage character in the series, and while I said I was going to judge him separately from legacy I will say Smash has a tendency to keep its more foundational, archetypical fighters that others are built upon. How many fighters have some derivative of PK Fire? Lucas, Robin and Joker at least.
And then frankly, I straight up don't think Earthbound is an irrelevant game or series. It's a complete, "retired" series yes - so what has been done since Mother 3 to keep it afloat? Honestly, quite a lot. All three Mother titles are on NSO and were met with sufficient fanfare and promotion. The series has been receiving an unprecedented amount of official merchandise. Its influence lives on through a number of widely successful indie titles. I feel like there is barely anything further that can be done here. Earthbound is a bigger deal today than it was 25 years ago when Ness first joined Smash... it is the figurehead of Nintendo cult classics. A path that Smash certainly helped pave the way for, but a success brought about by Smash Bros is still a success at the end of the day.