Here's my one and only confident prediction:
No DLC talk. At all.
People seem to think they're going to be talking all about DLC and what's ahead, but that's nonsense. That happened with Mewtwo because he was in-progress after the game was finished but before it was released, and they just wanted to say "Chill out, he's coming."
Otherwise, Nintendo doesn't really go "Hey here's all the stuff you get to pay for after the game comes out" before they release the game. It's a common practice with other companies these days (hell, last month's Spider-Man advertised its three-part episodic DLC before the game came out, and one of them came out just a week ago) but Nintendo isn't like that. They choose to focus on the base game first, and then worry about what comes afterwards.
For reference, Breath of the Wild didn't get its DLC announced (and released) until three months later at E3. Splatoon 2 didn't get its DLC announced until 8 months later in the March Direct earlier this year. Those things were soon enough after the game's launch that Nintendo could have brought them up before the games' releases, but they chose not to, because they wanted to focus on the quality and content of the final game.
This is also because, generally speaking, Nintendo holds onto announcements until relatively shortly before their release date. The exceptions to this were some of the games at E3 last year, especially Pokémon and Metroid Prime 4, but those were to assuage people's concerns about their existence, while making it clear that those games weren't coming out anytime soon. But they could have also announced Smash then, but they held onto it until this year, when it was actually coming out.
Not to mention that every time anyone at Nintendo was ever interviewed and asked about DLC, the answer was exactly that: Sakurai and team are focusing on the main game first, then worrying about what comes next. At San Diego Comic Con, for instance, IGN interviewed Bill Trinen and asked about DLC, and he said:
"Obviously that was a big part of the Wii U game, but part of Mr. Sakurai's approach is really 'let's focus on getting the game done.' And then once he has the game done, he'll start to make decisions about what he wants to do with other characters or DLC and things like that."
And there's a lot of game to worry about getting done. Even after ~50 minutes' worth of Directs and so much other information elsewhere, there's still so much about the game we don't know, and now we're getting a 40 minute Direct to cap it all off. With a game of this size and scope, the team doesn't have room to be thinking about all the stuff they'll do when it's done. It's already the biggest crossover game in history,
Which is why the insiders that are claiming "X character is DLC" raises warning signs about their statements' validity. With all these insiders and all these "leaks," we still don't know who is actually in the game right now or not. Yet these people claim to know who is going to be in the game in the future, before anything's even been worked on, which is highly unlikely.
Disclaimer: I could be wrong about this. Sakurai could introduce some unprecedented roadmap for all the content they wish to add to the game post-launch or something. Ultimate is already unprecedented in many ways, so there's always no telling what Sakurai is going to say or do. I'll be genuinely surprised if that happens, but I definitely don't expect it to.
So for now let's just be excited for all the crazy stuff we're going to see on Thursday that's going to be in the game when it's in our hands on December 7, because Sakurai's taken great measures to ensure that this game is packed when it releases, rather than hold things off for DLC in the future.
