The X-Men are coming to the Marvel Cinematic Universe eventually and there are almost sixty years of stories to choose from. A good place to start would be Grant Morrison's New X-Men, which contained some of the writer's best Marvel stories. Morrison unleashed their gonzo imagination on the X-Men and it paid dividends, as they created X-Men stories that hold up to this day.
Their first X-Men story, E Is For Extinction, contains a lot of great ideas that can be brought into the MCU's adaptation of the X-Men. However, not every single idea will work for an adaptation, as Morrison's out-there style might not work for general audiences.
10 MCU Should Adapt: The Story's Less Superhero-Centric Approach
One of the most interesting things about Morrison's time on New X-Men is they moved the team away from being a stereotypical superhero team. The team became a search and rescue team for mutants, defending them from threats, and bringing them to the school, where the team would teach them to use their powers.
This is a great approach to take, as it makes a lot of sense for them. It would also be good in that it would force the MCU to not tell the same kind of formulaic superhero tales they always do, which would actually be detrimental to X-Men style storytelling.
9 MCU Shouldn't Adapt: Putting Emma Frost On The Team
Emma Frost was once one of the X-Men's foes but E Is For Extinction brought her on to the team. She's more than proven her place as an X-Man over the years but a lot of her early time with the team was antagonistic towards Jean Grey. While she was fun and sassy, starting the team with her on it might be a bit much.
While her sarcastic and superior sense of humor would fit in with the MCU, putting someone on the team who would cause as much trouble as her right away isn't a great idea and changing her into more of a team player, especially at this point in her development, would make her a totally different character.
8 MCU Should Adapt: The Mutant Population Boom Would Help Explain Mutant's Sudden Existence
An interesting part of Morrison's run which E Is For Extinction introduced was the mutant population boom. Mutants were increasing exponentially, which was a big reason for the X-Men shifting their focus to helping mutants and the school—mutants needed a place to train and someone to help them more than ever.
Using this part of the story in the MCU would be a convenient way to explain why there were suddenly so many mutants. The story could begin with them suddenly showing up in massive numbers, which sparks the X-Men to go public after years of training to protect them.
7 MCU Shouldn't Adapt: The Discovery Of The Extinction Gene In Humans
There are two reasons the story is called E Is For Extinction and one of them is because Beast discovers that humanity will be extinct in four generations. This changes everything for the X-Men, as they realize they have to not only prepare mutants to inherit the Earth but also be ready for when humans find out and lash out against mutants.
To begin with, there's literally no way the MCU will adapt this plot point but even if it was on the table, it'd be a bad idea. Even Morrison barely touched on it throughout their run and it's just a hard thing to write around.
6 MCU Should Adapt: The Wild Sentinels Are Interesting & Modern Twist On Sentinels
E Is For Extinction introduces one of the most dangerous types of Sentinels ever: the Wild Sentinels. What makes them so deadly and interesting is the way their Master Mold made them, using all kinds of technology and designs from nature, like snakes, spiders, and birds, to create Sentinels unlike any fans had seen before. They were highly adaptive and extremely deadly.
While the MCU should probably change their look—the story's Wild Sentinels had a patchwork look because of all of the different tech used to make them—taking a page from these Sentinels, which came in a variety of shapes and sizes, is a perfect idea and one that could pay off in the future.
5 MCU Shouldn't Adapt: The Shi'Ar's Relationship To The X-Men
The Shi'Ar show up in the story's epilogue issue to take Professor X away, a plot point that led to more stories in the book. However, putting the Shi'Ar into an X-Men movie at an early stage or at all feels like a mistake. While they are a big part of the X-Men mythos, the X-Men are going to be hard enough to get right without going into their sci-fi elements too heavily.
The MCU has a team that deals with outer space and aliens already, so doing it with the X-Men as well would muddy the waters a bit too much. Beyond that, the X-Men are complicated enough without the Shi'Ar; throwing them in just gives Marvel Studios one more way to screw things up.
4 MCU Should Adapt: Cassandra Nova Is A Great Villain For The Movies
The X-Men have a lot of great villains and Cassandra Nova doesn't get enough credit for just how amazing of a villain she is. Nova's hatred of Xavier is very personal and her desire to wipe out the mutant race to get back at her brother makes her a perfect villain to pit the team against.
Cassandra Nova is tailor-made for the MCU; she's not a complex villain, so she fits in with the vast majority of the MCU's bad guys and she's massively powerful. Having her work with shady segments of the government to exterminate mutants is a great use of the character.
3 MCU Shouldn't Adapt: Cassandra Nova's Possession Of Professor X
One of E Is For Extinction's more interesting plot points is revealed in the epilogue issue—Cassandra Nova possessed Professor X. It makes for a great bridge to more stories in Morrison's run and also serves to show readers one of the worst things Xavier had ever done. However, using that in the MCU would be a mistake.
The MCU needs to establish Xavier first before they even think of doing something like this and even then, they probably shouldn't attempt it. Xavier is much more interesting as a morally grey character than he is possessed by a bad guy.
2 MCU Should Adapt: The Tone Of The Story
When Morrison took over the book, the name was changed to New X-Men and they certainly delivered on the promise of that name. Morrison was able to make the X-Men feel new in a way they hadn't felt in a long time. For the first time, the X-Men actually felt like the future, which was perfect for the type of story Morrison wanted to tell.
The X-Men are going to be a new team in the MCU and treating them like any old superhero concept is going to be a huge mistake. Adapting the tone of E Is For Extinction for the MCU would make the X-Men feel new and revitalize them after the Fox years.
1 MCU Shouldn't Adapt: The Genoshan Genocide Is Just Too Much
Beyond the human extinction gene being revealed in E Is For Extinction, the other reason it was called that was because of the Wild Sentinel enacted genocide of the mutant island of Genosha. Sixteen million mutants died in minutes and it was one of the worst days for the mutant race ever. This is not something the MCU should do.
Introducing Genosha just to be destroyed would be a mistake. It wouldn't have the impact it had in the comics and because it can't be magically undone like the Snap, it's just a bad look—an oppressed group having their home destroyed by racists would be a bad thing to do and the MCU doesn't have the writing talent to make it work.