Sakurai mentioned a while back that Zero Suit Samus would require rather specific cirumstances, these appear to be it. I wonder if doing it just once will unlock her. I imagine that under normal circumstances, Final Smash is a pretty rare item. It would reinforce how much you'd need to fight for it in a versus match since you can only use it once.

Before in Melee, it was do something specific, get challenged, defeat them, and it's unlocked. Let's just hope this is how to unlock her. Considering how much press her character has gotten, and considering she's supposed to have a very different fighting style, it wouldn't be right for this to be the only way.