Look at this snipet from an interview I dug up from 2007, or E3 06.
Nintendo: Will the single-player of Super Smash Bros. be the same as it was on the GameCube?
Masahiro Sakurai: No, we're going to change it. I think we're going to try and make a single-player mode that people can enjoy a little bit more than perhaps they did on the GameCube.
Shigeru Miyamoto: This is actually something Mr Sakurai and I have had a difference of opinion on since the very first Smash Bros. game. Mr Sakurai always wanted to have a very deep single-player game, and on the N64 version I just said to him, you know, we've got plenty of very deep single-player games, why don't you hurry up and just focus on multiplayer and don't worry about the single-player. And Mr Sakurai said no, no, no, I want to have some kind of single-player in there so I just said well, make it really short so we can focus on multiplayer and get the game done. And we kind of did a little bit of that on the GameCube, but a bit more single-player than that. This time we're getting a lot of time to focus on Smash Bros., plenty of time to develop it, so people can expect a very robust single-player game.
For the next Smash Bros Dreams article I'd like the story mode to be discussed. I remember very clearly from the original Smash days and Melee days how we all wanted more story. Brawl comes out and all we want now is less. Plus with all the demonizing Miyamoto gets now a'days I'd like to see their response to this. For me the less Kirby style platforming, the better. While Subspace seemingly feels like a typical Kirby game, running around with the different Smash characters in that platformer setting was exhausting. It never felt like a true platformer.