Warning: SPOILERS ahead for Spider-Man: Homecoming
Near the end of Spider-Man: Homecoming, Zendaya's character, Michelle, drops something of a bombshell on Peter and the gang: "My friends call me MJ." Those initials, of course, belong to the famous love of Peter Parker's life, Mary Jane Watson, played by Kirsten Dunst in Sam Raimi's Spider-Man movies, and by Shailene Woodley in The Amazing Spider-Man 2 (though her scenes were edited out of the final cut).
Now we know that Michelle is MJ, which means she's all-but-certainly destined to be Peter Parker's romantic lead as his corner of the Marvel Cinematic Universe continues to unfold. The classic red-headed Mary Jane Watson may not be part of the MCU, but a character bearing her initials would be a fitting nod to her legacy while forging a new path, similar to the "Robin" reveal at the end of The Dark Knight Rises.
However, in the months leading up to the film's release, Sony made the curious decision to attempt to conceal Michelle's true identity. They didn't just withhold information in a traditional, "just watch the movie and find out" sort of way, but they actively denied it, and even Zendaya herself "officially" stated that she was not playing Mary Jane.
MJ or Mary Jane?
With the final reveal in the film, one could argue that Zendaya wasn't really playing Mary Jane after all, since Homecoming may simply be using the legendary "MJ" initials to tease Michelle's status as Peter Parker's main love interest moving forward. However, that still seems like an awful lot of effort to conceal what is basically a non-spoiler, and to make Michelle "MJ" without really being MJ.
One of the main problems with the secrecy surrounding the supposed surprise is that Michelle is a scene-stealing background character, and not a central player in Spider-Man: Homecoming. It really wouldn't have made a difference if everyone had called her MJ or even Mary Jane throughout the movie, even if Michelle is a decidedly different character from any version of Mary Jane seen before. Aside from her initials, Michelle in Homecoming is entirely unlike the Mary Jane Watson comic readers (and devotees of the Sam Raimi trilogy) know and love.
On the other hand, regardless of the intent to develop Michelle as a brand new character within the MCU, giving her those famous initials has all but confirmed her as Peter Parker's inevitable destiny and one true love. Even though Kevin Feige has promised that Michelle's story isn't necessary beholden to the Peter/Mary Jane courtship with which the Marvel fandom is all-too familiar, only time will tell how their inevitable courtship plays out, and if there are any surprises in store for the eventual lovebirds.
Stan Lee Weighed In... In 2016
Interestingly, many fans who followed Spider-Man: Homecoming when it first entered development were not surprised by the reveal of Michelle's iconic initials; after all, when she was first cast, even though she was only billed as "Michelle," it was widely reported that she was actually playing Mary Jane, which led to an outspoken backlash from certain corners of the internet.
This backlash was fairly highly publicized, to the point where the legendary Stan "The Man" Lee weighed in on Zendaya's casting, all the way back in August of 2016, as did Guardians of the Galaxy director James Gunn. While Gunn prefaced his comments by stating that he didn't know for sure what part Zendaya was playing, Stan Lee's comments were less ambiguous, and he stated unequivocal support for changing the race of the character to fit the talented actor hired to play the role, all but confirming to many fervent Marvel followers that Zendaya was playing Mary Jane.
The point is, many fans went into the movie fully expecting Zendaya to be playing Mary Jane, and were, in fact, more surprised when she's first called "Michelle," than when she finally reveals herself as "MJ."
Why The Deceit?
Sony and Marvel went through a whole heap of trouble trying to cover up a secret which was not in need of a cover-up. Perhaps a simple "wait and see" response to the rumors would have fueled speculation and headlines, but the seemingly endless repetition of "she is absolutely not Mary Jane" is just silly in hindsight, even if it is technically true. Michelle is MJ, but she's not Mary Jane Watson. She was never going to be Mary Jane, but giving her the MJ moniker is a confirmation that she will have a greater role to play as Spider-Man's story continues to develop, though not necessarily with the same characterization and plot beats that comic book fans might be expecting from the character.
With all that in mind, was it a mistake for the movie to call Michelle "MJ," essentially cutting off the possibility of a true Mary Jane Watson introduction? It was certainly odd for the filmmakers to clamp down so hard on the true nature of Zendaya's character, the resulting anticipation of which made the "My friends call me MJ" line come across as something of an obligatory non-entity, especially since Michele is not Mary Jane, but is simply being positioned to be Peter's romantic interest in the next movie. In hindsight, maybe the movie would have been better served if Sony and Marvel hadn't so adamantly denied that Zendaya was playing Mary Jane, and just played coy until Homecoming's release. As it stands, the MJ reveal is, at worst, a needless – but harmless – twist which will clue fans in what direction the eventual sequel might take.