As "Avengers: Endgame" approaches, the Marvel Cinematic Universe remains the biggest movie franchise of all time. Can it keep up the success?

"Avengers: Endgame" marks a turning point for the Marvel Cinematic Universe. Veteran actors are likely to retire from their roles, and it will move beyond "Avengers" as its anchor franchise.

Business Insider talked to box-office, media, and comic-book experts about what the future of the MCU could look like and how it could sustain itself for years to come.

After the success of "Black Panther" and "Captain Marvel," diversity will be essential. For starters, Marvel is already developing its first movie starring an Asian superhero.

The Disney-Fox merger and Disney's upcoming streaming platform provide new opportunities and challenges for the MCU.

After 11 years, 21 movies, and $18 billion, the Marvel Cinematic Universe has experienced unprecedented success for a movie franchise.

"This is the hottest thing right now at the movies and in entertainment," Jeff Bock, an Exhibitor Relations senior box-office analyst, told Business Insider. "There's no escaping it."

He's right. "Captain Marvel" recently skyrocketed past $1 billion worldwide, and "Avengers: Endgame" is set to hit theaters on April 26. "Endgame," the culmination of those 11 years, is projected to shatter the box-office records its predecessor, "Avengers: Infinity War," set last year. And before the dust settles, "Spider-Man: Far From Home" will swing into theaters in July.

Read more: Early estimates say 'Avengers: Endgame' could shatter the opening weekend box office record

But after this year, the MCU will enter new territory. Disney CEO Bob Iger (the Mouse House owns Marvel) has said the MCU will focus on a "new franchise beyond 'Avengers,'" and Marvel Studios President Kevin Feige has said this era of the MCU is "gearing towards a conclusion" with "Endgame."

Some veteran franchise actors, like Chris Evans, who has played Captain America since 2011's "Captain America: The First Avenger," are expected to hang up their superhero suits after "Endgame." (Evans even joked in a recent Hollywood Reporter profile about the beloved character dying — a scenario that's not too far-fetched for comic-book readers.)

"A lot of it has to do with contracts running out and these actors, after a decade, wanting to go back to other things," David Betancourt, a reporter for The Washington Post's Comic Riffs blog, which covers comic-book culture, told Business Insider. "The core Avengers group is more or less disbanding."

But if it sounds as though the franchise could falter, Betancourt added: "The MCU has become such a strong brand, I don't think that will hinder it that much."

Chris Evans is expected to retire from his role as Captain America after "Avengers: Endgame." Marvel Studios

After 11 years, what's next? More diversity, for starters

Given the amount of secrecy surrounding "Endgame," not much is known about Marvel Studios' plans for the MCU after this year. But it does have eight release dates set for yet-to-be-titled movies through 2022, and at least six movies in the works that we know of:

A third "Guardians of the Galaxy" movie. Disney rehired the director James Gunn for it last month after firing him in July.

A Black Widow solo movie starring Scarlett Johansson.

"Doctor Strange" and "Black Panther" sequels, with the directors Scott Derrickson and Ryan Coogler returning.

"The Eternals," directed by Chloé Zhao ("The Rider").

"Shang-Chi," with the "Short Term 12" director Destin Daniel Cretton.

Read more: There are 6 Marvel movies in the works for after 'Avengers: Endgame' — here are all the details

With the success of "Captain Marvel," a sequel to that is also likely. And it would be surprising to not see a third "Spider-Man" movie after "Far From Home," unless Sony, which still retains creative and distribution rights to the character, reverses course.

Matthew Ball, a venture capitalist and former Amazon Studios executive who contributes to the media-analysis website Redef, told Business Insider that Marvel Studios had with Black Panther and Captain Marvel "clearly landed at least two big hit new stars with built-in audience demand" to lead the franchise forward.

As the first black character and the first female character to headline solo movies in the MCU, they highlight how essential diversity will be for the franchise's future. Both "Black Panther" and "Captain Marvel" grossed $1 billion worldwide.

"Captain Marvel" (2019). Marvel Studios

"They have to keep it fresh," Ball said. "The traditional model of Tony Stark and Stephen Strange is not infinitely repeatable. You need new challenges and perspectives. Their embrace of different storytelling and characters will help attract more talent. When you're putting out 30 movies, you never want it to feel like it's become a unit or a cog."

Victoria Alonso, Marvel Studios' production head, told Variety last month that "the world is ready" for a gay superhero in the MCU, and "The Eternals" is rumored to be led by a gay character. And Shang-Chi will be the MCU's first major Asian superhero.

"We're at the point where Hollywood is paying attention to a demand for more diverse casts, and Marvel and Disney are clearly listening to it," Shawn Robbins, Boxoffice.com chief analyst, told Business Insider, adding that a movie like "Shang-Chi" "has a lot of potential."

Fox and streaming provide new opportunities — and raise big questions

The Disney-Fox merger finally closed last month after Disney said last year that it would buy Fox for a whopping $71 billion. Disney now owns Fox's film studio, many of its television assets, its stake in Hulu, and the film rights to Fox's Marvel characters like the X-Men, the Fantastic Four, and Deadpool.

"As incredible as this streak of success has been, they've built it all from what was considered their second tier of characters," Robbins said. "Eleven years ago, outside of comic-book fans, nobody knew anything about Iron Man or especially about Guardians of the Galaxy. Now they have access to X-Men and Fantastic Four, which were the bedrock of comic books for decades.

"I never say never. It's hard to imagine repeating this streak of success. But they have the properties now to do it."

On top of the merger, Disney's set to launch a streaming service called Disney Plus later this year, and Marvel TV shows spinning off from the MCU are already in development. (A Loki show starring Tom Hiddleston has been announced, and others, like a Scarlet Witch series, have been reported to be in the works.)

Read more: After several 'Fantastic Four' flops, Disney should use its upcoming Netflix competitor to revamp the franchise

While the prospect of the X-Men and the Fantastic Four joining the MCU is an intriguing one, there are many big unanswered questions. How will Marvel usher in these new characters? How long will it take? Will audiences be confused? Is it willing to take the risk on the Fantastic Four?

In 10 years, Fox made three Fantastic Four movies, none of which was a resounding success story. 2015's reboot, again titled "Fantastic Four," made just $56 million in the US.

"Pop culture has evolved to the point where a lot of people know the difference between a [Fox] X-Men movie and what a Marvel Studios X-Men movie could be," Robbins said. "We've seen three versions of Spider-Man in less than two decades, and there didn't seem to be a lot of confusion. In general, audiences are very smart. Not to say that a studio can't have the occasional misstep with how to sell a character, but I don't think that's something we should expect from Disney."

Robbins added that he thinks it "won't rush an X-Men movie unless it feels like the right time to introduce the characters into the narrative of the MCU."

"They could wait five, maybe even 10 years," he said. "I think there's a strong argument to be made that the longer the wait, the more anticipation there will be for it. It gives these other Fox versions time to settle."

"Dark Phoenix," likely to be Fox's final X-Men movie, comes to theaters in June. Fox

If that sounds like a long time, consider that 10 years separated "Iron Man" and "Avengers: Infinity War," and that there's an X-Men movie coming to theaters this summer: "Dark Phoenix," likely the last of the Fox X-Men movies to hit theaters. (A spin-off movie called "The New Mutants," scheduled for release in August, is in limbo.)

And in the meantime, it's plausible that Marvel would sprinkle the former Fox characters throughout upcoming movies, or even use Disney Plus as a starting point, especially if Scarlet Witch (played by Elizabeth Olsen) stars in her own series. In the comics, Scarlet Witch is a mutant and the daughter of the X-Men villain Magneto. Because Fox owned the X-Men film rights, Marvel Studios couldn't use the term mutant — until now.

Read more: This chart shows how much longer 'Avengers: Endgame' is than other Marvel Cinematic Universe movies

For comic-book readers, that would be an exciting — but not shocking — revelation. The MCU has regularly used major comic storylines as inspiration, from "Captain America: Civil War" (based on the 2007 Marvel Comics event "Civil War"), to "Thor: Ragnarok" (the Hulk's storyline is heavily inspired by "Planet Hulk"), to "Infinity War" (the Thanos snap that wipes out half of humanity at the end of the movie occurs in the 1991 comic series "The Infinity Gauntlet").

But Betancourt thinks it's time for the MCU to move beyond the comics.

"I think they're at a point with the success they've had over the last decade where they can pull away from basing the big franchises off of popular comic-book events," Betancourt said. "They have enough firepower now that they don't need to go into the comic-book vault. Maybe they can start just leaning on the creativity of the people they have in-house to create something new."

No movie franchise can stay on top forever — or can it?

Franchises dominate the moviegoing experience these days, but the MCU is the only one that has landed on a winning formula where it can deliver up to three movies a year and all are box-office successes.

Even the "Star Wars" franchise hit a speed bump last year with "Solo," the first "Star Wars" movie during the Disney era that didn't crack $1 billion worldwide. (It made less than $400 million.) Iger said to expect a "slowdown" on "Star Wars" movies following "Solo."

The MCU has experienced no such speed bump. Seven of the nine MCU movies released since 2016 are among the franchise's 10 highest-grossing movies worldwide.

Shayanne Gal/Business Insider

What would it take for audiences to finally tap out?

"They'd have to make 10 'Ant-Man's in a row," Bock said. "And 'Ant-Man' isn't a bad series — it just doesn't captivate worldwide audiences. But they still make $600 million worldwide. For any other studio, that would be a massive hit."

That's why people shouldn't expect Disney, which distributed the three highest-grossing movies of 2018, to focus less on cinemas, even as it launches Disney Plus.

Read more: The legendary comics writer behind Marvel's Punisher and Ms. Marvel fears for the 'grim' and 'totally unsustainable' state of the comics industry

"Disney has placed a lot of importance on and stressed the theatrical experience, even while they're working on their streaming platform," Robbins said. "They'll make them coexist and save those popular characters for the big screen. You wouldn't see a Wolverine movie or an X-Men and Avengers crossover go straight to streaming. That would be a theatrical event."

But striking that balance could prove challenging. While Marvel Studios has perfected its big-screen cinematic universe, this is Disney's first jump into the streaming game. It will be integrating Fox assets at the same time, something that Barclays described in an October report as a potential challenge for Disney's streaming aspirations.

The Barclays analysts said that the company's pivot to streaming would "happen during what is likely to be a complex integration culturally between Fox and Disney."

But experts say the MCU will overcome the hurdles if it continues to play its cards right.

"If Kevin Feige and crew are still running things the way they have been, there's every reason to expect it could continue on," Robbins said. "It's hard to stay on top forever, but there's no reason to believe they can't do it ... But when you achieve this level of success, it takes a lot of care to keep it going."

Have a tip about Marvel or Disney? Contact the author at tclark@businessinsider.com.