Across the Spider-Verse looked to Avengers: Endgame for inspiration

But then kind of spreading it out and into two gives it that breathing room we all felt that it really needed to kind of go, 'Okay, what do you what do we need to set up in the second movie? And how can we resolve it in the third movie? Or not?' I don't know. We'll have to see. It was a really ambitious movie, and at the beginning, it was insanely ambitious, versus what it is now. It's still super ambitious, but it was like trying to fit two movies into one essentially. But now things can breathe a little bit more. https://www.youtube.com/watch?v=cqGjhVJWtEg&ab_channel=SonyPicturesEntertainment

The groundwork for the upcoming installment was set back in 2018 when Spider-Man: Into the Spider-Verse was released. It managed to coincide its storyline with the concept of the multiverse in a manner that hadn't been done before. The upcoming sequel works to build off that, by introducing several new characters that can traverse the multiverse, creating new alleys for additional story development. We got a glimpse of that with the most recent trailer where several Spider-People are being reintroduced alongside a familiar foe.

The Spot, the main villain from Spider-Man: Across the Spider-Verse, will appear and he's a lot more powerful than ever. Possessing unique powers that allow him to travel across the multiverse at his will with the help of interdimensional portals in order to commit heinous crimes. Implementing a character into the story with abilities of this kind enables further character development into a potential sequel in any of Marvel's alternative worlds.

Producers Phil Lord and Chris Miller hinted at this saying the introduction of Spider-Woman and Spider-Man 2099 into this sequel works perfectly in the grand scheme of things and it offers a great opportunity to transition Sony's Spider-Man universe into a proper MCU introduction.

A recent promotional poster might also suggest the presence of a variant of the Spectacular Spider-Man in the movie. According to the American novelist and ex-showrunner, Greg Weisman, seeing Spidey on a poster doesn't confirm the existence of the character in the movie. It remains to be seen how Spider-Man: Across the Spider-Verse can expand on its predecessor but if the tiny teases we already saw hold weight, we can expect a Multiversal story for the ages.

By splitting the movie and moving away from the Endgame format, the producers have far more freedom for the animation team Santos is leading and allowing the story to naturally breathe and progress into two movies, maybe even a possible third.

Who knows? Sony and Marvel Studios might collaborate and bring characters from Sony's Spider-Man Universe into the Marvel Cinematic Universe or vice versa. It might happen as soon as in the next Spider-Man movie.