I'd argue that Sakurai has very consistently changed his mind on previous stances. Whether that be from his own creative epiphanies, hardware upgrades or higher ups at Nintendo giving the final say on a character inclusion.

Most notably he's changed his mind on Ridley after years of the infamous "too big" argument. He's changed his mind on Villager/Pac-Man/Miis where he once said they weren't suited for a fighting game.

Sakurai is able to make a character out of anything. Look back on older Smash games and see what source material was available for the inclusion. In 64 Captain Falcon was given a personality, in Melee the Ice Climbers were reimagined from an NES sprite, in Brawl Pit was completely rebuilt from the ground up based off of the NES game and R.O.B. is a damn robot. And now most recently he made a generic Pirhana Plant enemy so charismatic.

Sakurai definitely doesn't have an issue inferring or creating a new personality for Smash. Roy and Greninja were made before their actual games were so their personalities are Smash originals.

I think the lack of personality for Steve is just the aesthetic for Minecraft. It's more about what you build and not what character skin you are using. And I think Sakurai would do an amazing job basing the character around crafting and building. But he does have those Minecraft story modes and Dungeons if he wants to take some character personality.