Sakurai here, please take a look at this. That's right, We've developed two story modes just to prove Diem wrong. Never talk **** about me on the internet again.
Hey, as much as I'm certain I'm right, I'd love to be wrong. I'd love for there to be a big SSE-scale story with Dark Samus and Ridley and Snake and Mega Man and Cloud. I was really disappointed we didn't get an SSE mode in Smash 4 (though in hindsight a little relieved, because that'd mean that Bayonetta, Cloud, Ryu, etc. would've been excluded).
If we get a full-blown story mode announced, and Sakurai announces it with the Dark Samus Amiibo sitting on his desk to taunt me, I'll get a tattoo of his face on my arm, and Smash Ultimate will be my all-time favorite game for the rest of my life.
IMO people are discounting story mode too quickly. In The direct Sakurai teased a hidden mode and said Rathalos would appear as a boss. Once you have the characters and world physics, story mode isn't that hard to throw together.
I didn't notice it at first (was too hype for Dark Samus), because I thought that Dracula and Rathalos were part of the Castlevania and Monster Hunter stages, like Yellow Devil in the Mega Man stage or Ridley in the Pyrosphere stage, but it's clear that their stages aren't for multiplayer and must be for another mode.
Adventure Mode in Melee was full of environments and stages exclusive to that mode, so that's what I'm expecting out of this game. A modest little string of environments and encounters like that, but maybe with a bit more polish and better presentation. Like you said, something just sort of thrown together. I'm excited for that, because I loved Melee's Adventure Mode, as barebones as it was. It was simple, but sometimes that's all you need. Let us just run through the Mushroom Kingdom or Hyrule Catacombs as Samus, blasting Goombas and Octorocks.
However, people seriously think that the trailers and file size means that SSE is confirmed. Despite the fact that Smash 4 had the same kind of trailers, and Smash Wii U had about the same file size with less content. These are the kind of people who probably expected a new Smash game soon, because they don't realize how much work is done behind the scenes to make these games as good as they are, making Ultimate such a genuine surprise. They think that a new story mode would be simple to implement, despite all the work already going into the game.
I made a thread on the Smash Reddit with my reasoning a couple weeks ago, and the top-voted reply was just "but we ultimate tho," so most people seem to believe it'll happen just because they want it, not because of any thoughtful reasoning or evidence. I shudder to think what the reaction will be when it's not what they're expecting. As
MasterOfKnees
said, it'll probably be the biggest complaint about the game, and for no reason other than that people aren't trying to be reasonable with their expectations.