Just like Peter Parker found out that Mysterio was actually the bad guy he has to face in Spider-Man: Far From Home, fans did not see it coming when an initial concept art for the movie considered giving Mysterio a different suit in the movie, and it's one you really wouldn't expect to see him in.
The said concept art came from Marvel Studio's head of visual development, Ryan Meinerding. As it turns out, Mysterio was initially given a suit that is strikingly similar in build with that of the Hulkbuster. If you recall, the Hulkbuster was seen in Avengers: Age of Ultron, it was then worn by Hulk himself when it also appeared in Infinity War.
The concept art for Mysterio's Hulkbuster suit was a bit bulkier, it was colored with shades of violet, and of course, finished off with the distinguishable fishbowl helmet.
The artwork actually originates from the book The Art of Spider-Man: Far From Home. According to Meinerding (via ScreenRant), most likely Mysterio having the Hulkbuster suit was an attempt to make the villain look more like a "tough, grizzled space marine," since he's the only person who escaped his dimension.
Regardless of whether or not the suit was actually used in the movie, it would be cool and quite intriguing to see Mysterio with the Hulkbuster. And quite frankly, if Mysterio did use it in the movie, there are even fewer chances that Peter Parker won't conclude him as a villain since it could remind him of Iron Man, well, the suit is made by Tony Stark after all.
As for Spider-Man 3, the movie is aiming for a release on July 16, 2021.