Star Wars' All-Inclusive Approach
Lucasfilm had traditionally taken a similar approach to Marvel, but in 2012 they were purchased by Disney, and were given the opportunity to redraw the Star Wars franchise's continuity. Execs decided to erase the old Expanded Universe altogether, and only a handful of projects associated with George Lucas - the films, the Clone Wars TV series, and a handful of episode adaptations - were retained as part of the canon. But from that point on, Lucasfilm established that everything else would be equally canon. Every tie-in novel, every comic, and every episode of an animated TV show would be just as much part of the Star Wars galaxy as the movies themselves. Lucasfilm formed a so-called "Story Group" to act as gatekeepers of the canon, carefully monitoring everything that happens to try to keep continuity in line.
At its best, this has allowed Lucasfilm to tell a single narrative that runs across different media. This was most effective with Rogue One, which saw Forest Whitaker play the part of Saw Gerrera, a character that had been introduced in the Clone Wars series. The film was supported by a prequel novel, Catalyst by James Luceno, and Alexander Freed penned a superb novelization. The books combined seamlessly with the movie to spell out the full history of Palpatine's Death Star project; meanwhile, when Rogue One proved a box office hit, the film was followed up by more tie-in novels, several comics, and the return of Saw Gerrera in Star Wars: Rebels. Lucasfilm's approach to canon had been proven remarkably successful.
There are, however, several problems with this model. The first is that Rogue One seems to have been an exceptional case; the tie-ins for The Last Jedi were relatively uninspired, and several were arguably misleading, encouraging fans to believe characters like Snoke were more significant than they proved when the movie was released. Behind-the-scenes drama on Solo appears to have damaged that film's tie-ins as well; Last Shot by Daniel Jose Older was frankly irrelevant, even though it was touted as an official movie tie-in. It's clear that coordinating a single story across multiple franchises requires a high degree of focus from the studio, likely the writers and directors as well, and that's simply not always possible. A second problem was demonstrated by Solo too. The unexpected Darth Maul cameo made perfect sense to viewers who'd watched Star Wars: The Clone Wars and Star Wars: Rebels; but it was absolutely meaningless to the vast majority of moviegoers.
The most significant issue is that this model probably won't be sustainable. The canon is building at a fantastic rate, and it will be increasingly difficult for the Story Group to keep track of all the details. Smaller contradictions are already beginning to build up. Meanwhile, creative ideas will become restricted because they don't fit with established canon. Right now, Charles Soule's Darth Vader series is revealing the secret history of Vader's fortress on Mustafar. But what if, in five years' time, a filmmaker has a stunning idea that explores a similar concept? They'll potentially be unable to do so, because of a comic book published years ago that won't have even been read by the majority of Star Wars fans.
Which One Is The Best Approach?
Lucasfilm's approach depends upon the idea of a dedicated Story Group, who carefully monitor continuity across the different mediums. That approach isn't one that could work with the MCU. Back in 2015, behind-the-scenes drama led Disney to split Marvel Studios away from the rest of Marvel Entertainment, meaning they're now separate Disney subsidiaries. The movies are made by Marvel Studios, the TV shows by Marvel Entertainment, and it's unlikely the two could cooperate enough to establish a similar Story Group that oversaw continuity. The relationship between Marvel Studios and Marvel Entertainment does seem to have improved over the course of the last year, but not by that much.
Curiously, both franchises have now faced the same challenge; what to do with a character who was killed in a movie, but resurrected in another medium? In the case of the MCU, Agent Coulson was killed off in 2012's The Avengers, but resurrected in Agents of S.H.I.E.L.D.. In 2015, Joss Whedon was presented with an opportunity to use Coulson in the sequel, Avengers: Age of Ultron. He chose not to do so; he felt it undermined Coulson's death, and would utterly confuse the majority of viewers who didn't watch the TV shows. In contrast, for Star Wars the character of Darth Maul was killed off in Star Wars: The Phantom Menace, but was resurrected in the animated shows. Lucasfilm actually chose to use the character in Solo, irrespective of whether or not most moviegoers would be confused. These two decisions highlight the difference in terms of the two approaches to canon. It's a matter of record that most viewers were utterly bewildered by the Maul cameo, proving that Whedon made the right call, and raising difficult questions for the Star Wars approach to canon.
The fundamental question is this: Which approach has the best chance of working out in the long run? Lucasfilm's seems like a smart move in the short-term, but as the canon builds it will prove very difficult indeed to keep it up. In contrast, Marvel's is sustainable. The two-tier model of canon allows Marvel Studios the freedom they need to make the best films possible without being constrained by other, lesser-known mediums. It will indeed sometimes mean that elements have to be written out of canon; so far it's only happened to two tie-in comics, but there could be a more significant impact if Agent Coulson's backstory in Captain Marvel differs too much to the one we've seen presented in dialogue and flashbacks in Agents of S.H.I.E.L.D.. No doubt that will frustrate the most hardcore fans, but Marvel Studios will consider that a price worth paying.