Even though Sakurai has "the final say", he can be persuaded. Shortly after Corrin was revealed, when it came as to why he was added, Sakurai said that "look man i wasn't sure if i should add this one, there are already too many of them Fire Emblemz" and then his team went like "no no man you should totally do this". Literally only went for it because his team pushed him to do so.
Or how about the time Kojima begged Sakurai to add Snake in Smash.
or the time time where there an entire campain happened to add K.Rool in Smash 4, and continued into the Ballot (#KrocTheVote anyone?)
He may have the final say, but he sure as hell can be persuaded. and if he can be persuaded by his team or people on the internet that voted for a singing krocodile, and sure as hell can be persuaded by his higher ups at Nintendo. I mean
Exececutive Meddling is a thing, and while im not an advocate for it at all, i wouldn't be surpised if it happened (assuming it hasn't happened already)
Just because it hasn't happened before doesn't mean it can't happen now.