The Marvel Cinematic Universe is already teasing the future of the franchise through an Easter egg at the end of Spider-Man: Far From Home. The 23rd film in the series also marks the official end to Phase 3 of the MCU, and Marvel has yet to officially announce what's coming in Phase 4.
Spider-Man: Far From Home takes place shortly after the events of Avengers: Endgame. Peter Parker (Tom Holland) is still grieving the loss of Tony Stark, while the rest of the world is wondering if the Avengers still exist. During his school trip to Europe, Peter intends to leave his Spider-Man alter-ego at home so he can fully enjoy time with his friends. Of course, his plans go awry thanks to a group of villains called Elementals and the arrival of a new "superhero" called Mysterio (Jake Gyllenhaal). The Elementals turn out to be a ruse cooked up by Mysterio, also known as Quentin Beck, and other disgruntled employees that once worked for Tony.
Peter manages to take down Quentin and his advanced technology while also saving London from complete destruction. He also gets the girl as Peter and MJ (Zendaya) finally share their mutual feelings for each other before heading back home. Once they are back in New York, Peter leaves for his date with MJ and swings through the city. During his travels, Peter passes the old Avengers Tower, which was apparently sold when Tony moved the Avengers headquarters to upstate New York. Peter sees MJ standing on the sidewalk so he lands directly in front of the building which is still under construction. One of the construction signs is a fun nod to the MCU and its upcoming Phase 4.
The sign reads "We Can’t Wait to Show You What Comes Next" along with the numbers "1-2-3-?" - a clear reference to the upcoming fourth phase of the MCU. There is no confirmation regarding plans for Phase 4 but it will include movies such as Black Widow, The Eternals, and Shang-Chi. Marvel Studios President Kevin Feige plans to unveil more details regarding the next chapter of the MCU in coming months, likely at San Diego Comic-Con or D23.
Another possible explanation to the sign is the anticipated arrival of the Fantastic Four into the MCU. Now that Marvel has gained the movie rights to more Marvel characters following Disney's acquisition of 20th Century Fox, fans are anticipating an expansion of the MCU to include the comics' first superhero family. The old Avengers Tower could potentially be turned into the Fantastic Four headquarters, either the Baxter Building or Four Freedoms Plaza.
So how will Spider-Man play into Phase 4? There will most likely be another Spider-Man solo movie, but not right away. The first post-credits scene in Spider-Man: Far From Home indicates that Peter has more trouble ahead, as a doctored video was released that makes it look like he killed the seemingly innocent Mysterio. Peter's identity as Spider-Man was also unveiled to the public, so any chance of living as a normal teenager is seemingly lost forever.