Technically he did call them Smash 4 and Smash 5. And there's a Smash 6 whatever it is at works in the Bandai Namco studios at probably this exact moment with the people they've already hired.
Smash 4: 3DS, core roster was what they could initially achieve for this system in the given time frame. They realize they must release it with as much content as they can. Nintendo makes them aware of an improve 3DS coming down the line, maybe even spawned from the limtations ran into making this version.
Smash 5: Wii U, with the new plan in place, Sakurai sets out to finish the characters he wanted to finish for 3DS and incorporates them into the Wii U roster. He leaves the production to take a rest.
Smash 6: New 3DS, the completed and new version of the final product that was released as the Wii U version. Bandai Namco hires new people to finish this project, as well as any DLC for the Wii U and the RE-Release for New 3DS.
A scenario like this is not entirely unlikely but it'd not be a first in the fighting game making industry. Just Nintendo history.