Of course, it doesn't look like Carol will get off on the wrong foot with Law's character -- at least, not right away. “These extraordinary powers she has, he sees them as something of a blessing and something that she has to learn how to control,” Law teased. “That’s a motif throughout the piece, the element of learning to control one’s emotions and to use your powers wisely.” Nevertheless, it's worth remembering that Marvel rarely makes direct adaptations; the studio typically takes a character concept from the comics and works it to fit the film plot, while staying true to the spirit of the character.
It wouldn't be surprising, then, if Yon-Rogg didn't start out as a villain, only to become one later on. In fact, Doctor Strange pulled a similar stunt; Karl Mordo was originally a mentor and ally to Stephen Strange, but turned villain when the foundation of his faith was shaken. Captain Marvel could certainly take a similar approach. After all, we know something will happen to Staforce that causes Ronan to go from a respected Kree officer to an extremist zealot. Ronan could very well drag Law's character down with him, leading him to become a villain for potential sequels set in the present day.
Besides, Yon-Rogg has a sillier motivation for disliking Mar-Vell in the comics. Their rivalry boils down to another person altogether: Una, a Kree medic. Una served on the Helion with both Mar-Vell and Yon-Rogg but fell in love with Mar-Vell, causing Yon-Rogg to become deeply jealous. So, originally, Yon-Rogg sought to kill Mar-Vell in order to have Una all to himself. Ultimately, Una was killed in the crossfire when Yon-Rogg attempted to execute Mar-Vell. If Law is indeed playing Yon-Rogg, then, it would make sense if his hatred for Carol -- who seems to be standing in for Mar-Vell here -- took root in a different way.
Notably, Yon-Rogg was also the villain of the Kelly Sue DeConnick and Dexter Soy arc on the character, where Carol traded the "Ms. Marvel" moniker for "Captain Marvel." This was a transformative storyline for Carol; in addition to changing her name, she ditched her black swimsuit costume for the red-and-blue ensemble she'll be wearing in the movie. Since the film is already drawing so much influence from this run, it wouldn't be surprising if it tapped Yon-Rogg as the villain too, especially where the two have such an extensive history with one another.
If the identity of Jude Law's character wasn't meant to be a surprise, Marvel Studios would have released it by now. However, thanks to their secrecy, it seems more and more likely that he won't play Mar-Vell -- but there is another Kree that fits the bill: Yon-Rogg. By casting Law as Yon-Rogg, Captain Marvel could establish a layered antagonist who has a complex relationship with Carol Danvers for a potential sequel down the line. Even as she battles the Skrull, Carol may find herself at war with one of her closest friends and allies; it certainly wouldn't be a first for the Marvel Cinematic Universe. We'll just have to wait until March 2019 to find out for certain.
Directed by Anna Boden and Ryan Fleck from a script they wrote with Liz Flahive, Carly Mensch, Meg LeFauve, Nicole Perlman and Geneva Robertson-Dworet, Captain Marvel stars Brie Larson as Carol Danvers, Samuel L. Jackson as Nick Fury, Jude Law as Mar-Vell, Clark Gregg as Phil Coulson, Lee Pace as Ronan the Accuser, Djimon Hounsou as Korath the Pursuer, Gemma Chan as Minn-Erva, Ben Mendelsohn as Talos and Lashana Lynch as Maria Rambeau. The film arrives March 8, 2019.