Why Does Maul Sound So Different?
To fans that haven't seen Darth Maul appear since The Phantom Menace, it may be weird for him to not still be voiced by Peter Serafinowicz, but for anyone invested in Star Wars animation, Maul has had numerous episodes of The Clone Wars and Rebels over the past decade where he's voiced by Sam Witwer.
The former Sith's transformation from the stoic Sith apprentice to the more verbose and expressive Force wielder shown in animation is a marked transformation but makes sense considering his mental break and restoration. Physically, Maul was performed again by his original live-action actor, Ray Park, making the combined vocal and physical performance one of the more fascinating blendings of multiple eras and formats of Star Wars in the Disney era.
When Will Maul Return?
This is the big question. Maul's in inclusion in Solo clearly wasn't there for Solo but for the future movies it sets up. The seal has been broken and Maul is alive and well in live-action. There's clearly plans to see more of him in the future. But when and where?
Unfortunately, there are still no confirmed titles beyond Solo other than Episode IX, and even that doesn't have a title. We know a number of movies are incoming though. Plans for a Boba Fett movie were just revealed (although have not been confirmed by the studio), persistent rumors suggest an Obi-Wan Kenobi movie is in the works, there's multiple films in development under the eyes of Rian Johnson and the Game of Thrones duo, David Benioff and D.B. Weiss, and finally a slew of other characters are having stories developed.
Since Maul is a major figure in the shadowy underbelly of the galaxy's criminal world, he could play a part in the Boba Fett movie, so long as it takes place before Maul's death; the Kenobi movie is doubtful, unless they adapt a story already told in animation, which isn't out of the question, but not likely; and without knowing what the Benioff/Weiss or Johnson movies are about, it's impossible to know. Then, of course, there's always the chance he could be getting his own spin-off.
It seems most logical to assume that Solo is setting him up for its own sequel, but the notion of Darth Maul being a major Han Solo villain doesn't completely line up with what we know of Han, and besides, the movie set up a very different sequel with Han doing a job for Jabba.
Wherever he shows up next, it's an exciting time for Star Wars fans. Maul has always been seen as one of the coolest characters with the poorest utilization in live-action. His design instantly had people excited for his appearance in The Phantom Menace, only to have minimal screentime and die at the end. His revival in animation and comics has seen a strong response, so hopefully that means his cross back over into live-action provides the big screen redemption that fandom has been craving for 20 years.