Well, there’s core team and appearances.
At this stage I’d go with the Krakoa story, so I’d hit the ground running with a flashback of the ANAD team, with Cyclops, flying in the jet to rescue the rest of the O5 team + Havok and Polaris. Close ups on Ororo, Logan, Kurt and Piotr and we get flashbacks (within the flashback) of them being recruited by Xavier and Scott for the mission, and those flashbacks also explain what Krakoa is too. You also have some others on the jet in Banshee, Sunfire (maybe make her female/Sunpyre) and Thunderbird, but it’s too many characters for recruiting flashbacks for all of them, so those three don’t get one.
They land, have a big epic Kong: Skull Island like adventure on the island with it trying to kill them in various ways (like in the comic), Thunderbird dies somehow, and ultimately they rescue the rest of the X-men and escape. Instead of blasting Krakoa into space, however, maybe Polaris and Ororo team up to “sink the island” under a massive tidal wave. As they’re leaving, Scott is holding a Krakoan flower and he gets a telepathic inquiry from Xavier, “Did you get it?” to which he mentally responds, “Yes. I hope it was worth it.”
Fast forward to the present, and we hit the ground running with the House of X set up in the present day and the looming U.N. vote on sovereignty of the mutant nation. Lots and lots of tidbits in here in the form of dialogue and news media. You learn that the X-men lived at a school before Xavier set up shop on the island, that Magneto is considered a mutant terrorist, etc. There is even some dialogue between Xavier and Emma Frost about how they used their gifts to shield mutants from the world at large for a long time. Stuff like that to establish this set up for mutants in the MCU.
Main cast members would be...
- Xavier
- Magneto
- Emma Frost
- Cyclops
- Jean Grey
- Storm
- Nightcrawler
- Wolverine
- Colossus
- Mystique
Orchis would be introduced and the looming threat of Mother Mold in space. We’d find out they have Sentinels and basically this giant factory orbiting the sun manufacturing them. We discover this via information stolen by Mystique and Magneto’s Brotherhood, mutant terrorists, including Sabretooth and several others. Creed is captured, and we get the scene where Emma uses diplomatic immunity to extradite him to Krakoa.
The latter seven (Cyclops, Jean, Storm, Kurt, Logan, Piotr and Mystique) assault the base, and die much like we saw in House of X #4. Except it’s Storm who puts Jean into the escape pod and tries to fight off the Sentinels and Orchis soldiers. They are close, and this is an emotional moment of sacrifice between best friends. The rest plays out like it did in the comic pretty much. This whole scene is a real holy $#!t moment for viewers.
Back on Earth, we see the emotional fallout in the faces of the X-men in the command and control room on Krakoa... Xavier, Beast, Iceman, Psylocke* (Kwannon version), Forge, Jubilee, Rogue, Bishop... maybe a few other cameos. It wraps up with the Krakoan nation state being recognized by the U.N. and Emma Frost establishing the Hellfire Trading Company to trade their precious flowers with the nations who signed off on it. It’s an optimistic tone for the future.
The mid-credits scene, however, is the kicker. That’s the whole resurrection scene where we see how Xavier has been using Cerebro to record the memories of all mutants on Earth, and it’s him and Beast overseeing the resurrection process. He mentions to Beast having had to make an unsavory deal with Nathaniel Essex to gain access to his vast DNA database, and we get introduced to “The Five” and some exposition of how this works, but highly simplified. Basically, the combination of these five mutants’ unique gifts using the DNA and memory back up can bend reality itself and defy death, restoring what was lost to us including the anima — or the very essence or soul — of the deceased. We end with Jean bursting out of one of the pods and Xavier, smiling, saying “Welcome back.”
The after credits scene sees Sinister springing Creed from his prison on Krakoa, setting up the Marauders and a modernized version of the Mutant Massacre for the sequel. This will introduce Gambit, and it sees the X-men trying to stop Sinister’s rampant genocide in the sewers. We also learn that he’s trying to create super mutants by combining DNA of powerful mutants, and we even see baby Nathan Summers in a tank at one point, setting up Cable at some point down the line. Perhaps in the third film where we get Apocalypse and the Horsemen, or maybe save that for an X-Force spinoff loosely based on Remender’s Uncanny X-Force. Something like that.
*I think I’d go with the current setup of Psylocke being Kwannon for these films. We’ll meet Betsy Braddock in the sequel, but as the head of Excalibur, a UK super team like the Avengers, and sister to Captain Britain its leader. This sets her up for more in the MCU down the road, where something could happen to Brian and she becomes the new Captain Britain. Maybe even an Excalibur spinoff film.