Providing a satisfying ending to The Fast Saga in Fast & Furious 11 would be difficult if it doesn't feature a return from Paul Walker's Brian. As one of the original cast members of the car-centric franchise, the actor's untimely death in 2013 significantly impacted its storytelling. But, instead of killing off the character on the screen, Universal decided to give him a more satisfying send-off in Furious 7 by simply having Brian retire from the crew's operations.
Since then, there have been few references to Brian in The Fast Saga. In order to properly sell the idea that he's simply enjoying a quiet life with his family, even Jordana Brewster had to retire from her role as Mia by not appearing in Fate of the Furious. But as the events of Fast & Furious 9 became very personal to the Torettos with the return of their estranged brother, Jakob, she eventually had to come out of hiding and join the "la familia's" latest mission. While her re-emergence was a welcome development, especially since she finally got to spend time on screen with Letty, questions about Brian understandably came up. It turns out, he's alive and well; he sat out the operations to take care of his and Dom's kids.
Fast & Furious 9 doubled down on the idea that Brian is fine. As Dom's crew gathered for their regular post-mission barbecue, with Mia already in her brother's home, her husband's signature blue Nissan GT-Rs zoomed through the streets, indicating that he's on his way to join his old crew, as well. If Mia remains involved with his brother's operations after their recent bout with Jakob, there will be continued hope that, somehow, Brian, too, will appear physically. But while director Justin Lin and his team can get creative in explaining why he chooses to opt-out of the "la familia's" future endeavors, bringing him back for Fast & Furious 11 is mandatory. As with long-running narratives, there's massive pressure for Universal to stick the landing for the car-centric franchise. And there's almost no way for the filmmaker to deliver a satisfying ending to The Fast Saga without one of its main characters.
Sadly, however, Walker is no longer around to reprise the role. But, that doesn't mean that this cannot be done. When the actor died in the terrible car crash, production for Furious 7 was still ongoing, so he wasn't able to finish his work in the film. For a while, filming on the project was halted as Universal decided how they were going to move on from the tragedy. They ended up rewriting the character's fate in the narrative, giving him a happy send-off instead. To be able to accomplish this, however, Walker's brothers got involved as doubles. Given this, it's not outside the realm of possibility that they will, once again, gamely join Fast & Furious 11 just so Brian can factor in it.
Looking back, it's best that Walker's character didn't explicitly appear in F9. It's also safe to assume that he will continue to be absent in Fast & Furious 10, but that, too, is fine, as long as he re-emerges for Fast & Furious 11. Granted that he still won't be able to actively join Dom's mission given the limits of CGI in recreating Brian. But despite this, just as long as he ultimately reunites with the "la familia" in any way possible would already be a big treat for fans of The Fast Saga.