No it cannot change. Just like Shrek will never change. Or Spongebob. I'd wager more people on this earth know who Mickey Mouse is and have no clue who Goku is... Still Mickey Mouse will never be in...just like Goku. It isn't happening in any realistic timeline.
We'll live to see Waluigi in before Goku.
Indeed we may. And for the record, I don't feel Goku is a necessary addition to Smash at all. But people should be allowed to want him. The reason I keep bringing up Geno in this example is that the character would have no chance whatsoever on his own merits. Yet sheer fan devotion has put him in the spotlight to the point where even Sakurai has had to acknowledge it. Fan demand alone, because that is literally the entirety of Geno's push. If he gets in, its because enough people asked for it.
There's one person and his team alone that can decide what a "realistic timeline" is. And that's Sakurai and Sora. And if he decides to flip the table and re-write the rules and add Goku, he will. Period. No one but him decides that. And as long as a human being is capable of agency and autonomy and has the power to decide something, that thing becomes theoretically possible. Thus, no matter how unlikely it is, why not humor the possibility and throw his fans a bone?
If Sakurai was a robot who was hardwired to obey his own pre-set rules, we could all say with certainty that Goku, a breech of said rules, is impossible. But he's not.
I used to think Cloud was impossible. Didn't even consider or speculate him because it was so farfetched. And now here we are.
Let people want, who they want. I want Dixie, Sephiroth, Tiki, Isaac, Banjo, Black Knight. Will I see any of them? Maybe not. Doesn't mean I can't hope. Stop trying to stomp all over people who hope for Goku. Not just you, but everyone.