I kind of already replied to someone below.... but basically Iwata was the bridge between Sakurai and his former employer, Nintendo. I think Iwata was able to manage Sakurai and his moodiness, basically. I mean, Sakurai has that credibility to direct and make profitable software, but I don't know if he will without someone like Iwata to accommodate him.
And I'm not saying he will release a PS4 exclusive... unless he made some sort of deal. I'm just expectint something multiplatform instead of a Nintendo exclusive again. I mean... Project Sora was mostly Nintendo employees but that dissolved after Kid Icarus and Brawl... and then Nintendo partnered with Bandai-Namco to help Sora Ltd make Smash 4.