Ever since his first appearance in Thor, Loki has been undoubtedly recognized as one of the most powerful characters in the Marvel Cinematic Universe for the past decade. From his mischievous and complex relationship with his brother, Thor, to his evil scheme to destroy Earth in The Avengers, Loki is a character who inhabits both good and bad qualities. Besides Iron Man, Captain America, and Thor, the God of Mischief has been in the MCU for a long time.
While Loki still has more to give, especially with his immensely popular Disney+ series (with season two recently confirmed), this could mean that Marvel movies may have some difficulty in developing other Marvel characters since Loki's character depth is immense. With Tony Stark and Steve Rodgers ending their long and successful runs two years ago in Avengers: Endgame, Loki is now one of the longest-running MCU characters left, along with Thor and a few others.
What makes Loki such a unique Marvel character is his ability to resurrect himself. There have been a number of times, including the first two Thor films, in which it appeared he met his demise. He is also very charismatic, like Tony Stark, when it comes to getting what he wants, such as the throne of Asgard, or world domination, and has powerful methods of persuasion (including with the use of his septor).
The only issue with adding more of Loki to future Marvel films is that his presence may take away the spotlight from other characters, especially new superheroes. His new solo series, Loki, is, however, effective in establishing new characters. Sylvie, a female variant of Loki, has terrific chemistry with the God of Mischief, despite their opposing viewpoints. Mobius, a TVA (Time Variance Authority) agent, has also become Loki's friend, influencing him to think about his past and reflect on his misdeeds.
In terms of films, new features with Spider-Man and Doctor Strange will expand on the multiverse that started in Loki. There are also new superheroes such as Shang-Chi and the Eternals that will likely involve more supernatural elements and can be as cool and appealing as Loki. There are also certain characters coming back, like a new iteration of Blade, that could make an impact on phase four or five of the MCU.
Despite this expansion, the question is how involved a powerful and impactful character like Loki could be in future films. Will he be relied on more, like Tony Stark, Steve Rodgers, and Thor were, to be a leader of a new army? Will new characters interact with Loki as a hero or villain?
Since there has already been a major villain like Thanos, and Loki has most likely shifted from villain to hero thanks to the character development in his series, Loki would serve better as a hero seeking to help other upcoming heroes. Loki will undoubtedly have a major presence in future Marvel films in order to solve the multiverse dilemma, and this will test filmmakers in terms of how many other Marvel characters will be involved, and how much screen time for each role.
In the past, Tony Stark/Iron Man and Steve Rodgers/Captain America took up the majority of screen time in their solo films and in the Avengers series, which took away some character development from characters like Bucky Barnes/Winter Soldier, Sam Wilson/Falcon, Bruce Banner/Hulk, and Vision. This is the problem that could happen between Loki and other heroes in the future. Loki has that ability to command the screen and steal the show, especially since his character has grown so much since Thor.
The actor himself, Tom Hiddleston, is also fairly young and has the strength, charisma, and screen presence to drive Loki's journey much further. However, another difficulty that filmmakers have to contemplate is how to cover themes related to Loki that may resemble other Marvel characters. For instance, the theme of brotherhood and sibling rivalry has been fully established, both in dramatic and comedic ways, in Loki and Thor's relationship, as well as jealousy between partners. These themes could also be found when Fantastic Four and X-Men are potentially rebooted (and have been covered in previous adaptations).
Loki has also established the theme of guilt because he's a killer who feels remorseful for the crimes he's committed against humanity and intends on redeeming himself by doing good. Black Widow and Wolverine relate to this because these characters are assassins who have taken down a lot of people, and try so hard to defeat evil and erase their horrifying pasts. If Wolverine is brought back, how will the familiar concepts of vengeance fit into future films, and could the X-Men or other Avengers work together in the MCU alongside a powerful character like Loki?
Iron Man and Captain America had long, successful runs because their characters were always recognized as leaders who were intelligent and emotionally invested in the MCU. Loki (and Thor) are also viewed in this way, but can go in other directions because, since they're gods, they can last for a while, inspiring other outcasts like the ones in Thor: Ragnarok.
Whether or not familiar and unfamiliar Marvel characters will join Loki or fight him, the God of Mischief (an MCU veteran) will continue to have a tremendous impact on phase four, and so on. Whichever direction Loki's story goes, his character will continue to have depth in terms of redemption, personal relationships, and time. Future Marvel films need to find a balance in how to display old, new, and/or rebooted heroes and villains in order to keep up with the dynamically charismatic Loki.