Even before Captain America: Civil War was released, Marvel fans knew that Iron Man and Spider-Man would form a bond in the midst of the conflict due to fighting on the same team and the former mentoring the latter. So when it was announced that Robert Downey Jr. would reprise Tony Stark in Spider-Man: Homecoming, many were pleased to see that their relationship will grow. What is still a mystery is why exactly Tony is appearing in the Web-Slinger's first MCU solo movie. Marvel is staying mum on the subject, but a possible photo from the set suggests that Tony's in town for a new Stark Expo presentation.
Having concluded principal photography in Atlanta, Georgia, Spider-Man: Homecoming has been shooting in New York over the last several days, and one Redditor posted a set picture supposedly showing flyers advertising a new Stark Expo that will happen from October 17-27, 2018 in New York City. If this photo was indeed taken on the Spider-Man: Homecoming set, then that would provide enough reason for why Tony Stark is in Peter Parker's neck of the woods, as the Avengers are no longer based in Stark Tower post-Avengers: Age of Ultron. That said, it's unclear whether the Stark Expo is actually happening during Spider-Man: Homecoming (thus placing the movie one year ahead of when it's released) or if it's being advertised a year ahead of time. Either way, while he's involved with that, he can also take the opportunity to meet with Peter again.
Tony's father, Howard Stark, hosted the first Stark Expo in 1943 during Captain America: The First Avenger, and just like every Expo held afterwards, it brought the greatest minds from around the world to demonstrate cutting-edge technology that would benefit humanity. Howard held the last Stark Expo himself in 1974, but 36 years later, Tony hosted a new one during Iron Man 2. Unfortunately, during the presentations, he had to contend with Ivan Vanko and Justin Hammer, and the Stark Expo was eventually directly targeted by Vanko when he took control of Hammer's drones and War Machine's armor. So yeah, the Stark Expo relaunch didn't go exactly as Tony planned, but eight years is enough time to try again, right?
It's worth mentioning that even if this new Stark Expo is legitimate, it may not be the only reason for Tony Stark's involvement in Spider-Man: Homecoming. It was rumored last month that The Tinkerer, one of the movie's main villains, is an ex-Stark Industries employee who was personally fired by Tony. Eager to prove his former boss was wrong about him, Tinkerer will provide Spider-Man: Homecoming's other two baddies, Vulture and Shocker, with special technology to commit crimes. It wouldn't be surprising if while Tony is in New York City (with his buddy, Happy Hogan) working on the Stark Expo, these antagonists target him, leading Spider-Man to intervene and reunite with his fellow Marvel tech whiz.
Spider-Man: Homecoming will spin its web in theaters on July 7, 2017.