
The most likely possibility is that the Ultimate Peter Parker is coming back. But it can also be the first crossover between the Ultimate Universe and the Classic Marvel Universe.
Marvel hasn't done a crossover in the eleven years since Ultimate Spider-Man #1, although they hinted at the possibility at the beginning of Mark Millar and Greg Land's Ultimate Fantastic Four run. That was a swerve which led to the introduction of the Marvel Zombies world. Though the Marvel Zombies interacted with Black Panther, so there's at least some precedent for one of the Spider-Man to travel into the world of the other. There was also the recent Shattered Dimensions video game, featuring the Marvel Universe Spider-Man, the Ultimate Peter Parker, the Noir Peter Parker and Spider-Man 2099.
A common complaint about the crossover is that Marvel promised they wouldn't ever tell that story. A quote that's referenced a few times in online discussions today is Quesada's alleged comment that the day Marvel does a crossover between the two universes is the day they run out of ideas. To be fair to Quesada, I haven't been able to google the exact quote, although I do vaguely remember hearing something like that.
If he said, that's not a reason to reject a story that could be exciting. When the idea of an X-Over was first broached, it was during a time when the Ultimate Spider-Man was Peter Parker, and a team-up would feature a teen meeting an alternate version of himself as a slightly older guy. But the dynamic has changed significantly, and I wouldn't mind seeing a crossover between the 616 Peter Parker and the Ultimate Miles Morales. It would be an interesting for to have Peter go to a world in which he's essentially Joan of Arc, a young martyr who inspired millions. And for Miles, it would fascinating to see the guy his role model would have grown up to become.

Honestly, I think it's better to keep the Ultimate Peter Parker dead, and to never bring him back. The Ultimate Peter's death is meaningful for the Ultimate Universe, almost the 21st Century version of the Death of Gwen Stacy. It's something that distinguishes the Ultimate Universe from the Classic Marvel Universe, suggesting to readers that this is an entirely different playground than the one they're used to.
Bringing back a teenage Peter Parker to a world in which he's a celebrity would generate some story ideas, but it seems like something that would be exhausted rather quickly. And it might kneecap his best-selling replacement, as the character's not as important in a world with Peter Parker. It would show that the Ultimate Universe isn't that different from the Classic Marvel Universe. But a team-up between the Classic Peter Parker and Miles Morales could highlight what's made both characters and world unique.