Matthew Vaughn is also similar in style to Gunn as a director, although an argument can be made for him being even more controversial in his brand of comedy. We saw this in the Kick-Ass and Kingsman franchises, where he also used heavy humor, but spliced into even more high-octane sequences. He was supposedly in talks to helm a Man of Steel sequel too but with no movement on that front, Marvel can offer the Guardians franchise as a replacement.
He's one of the most respected directors in the comic book movie realm, too, and some fresh perspective could be a good thing. He knows about franchising, and sets the stage for long-term stories, which would reassure fans hoping he can recapture Gunn's magic. If they're worried about him handling an ensemble film, well, look no further than how he restored faith to Fox's X-Men universe with First Class.
A lot of what we've seen transpire on-screen stems from Nicole Perlman, who was responsible for the first Guardians script before Gunn came aboard. She was enrolled in Marvel's screenwriting programme in 2009 and chose the Dan Abnett and Andy Lanning comics (some of the most critically praised books) to influence her work, which ultimately led to Thanos' victory in Avengers: Infinity War.
She's just as big a fan as Gunn and knows the franchise very intimately. Perlman is still heavily involved in the MCU cosmic, as a writer on the upcoming Captain Marvel movie too, so if the studio decides to take a risk, she could move into the director's chair and add to the MCU's burgeoning female movement. This could be a great success story of Disney giving a female writer her first big break as a director, and who better than the person who helped get fans hooked on space's most heroic rogues.