There's one major She-Hulk: Attorney at Law, it won't be long before mutants are interacting with already established MCU superheroes.
Prior to Marvel regaining the rights to the mutants, Logan. While these three projects were positively received, there's one storyline that has been adapted more than any other and has been met with an overwhelmingly negative response each time.
Both 2006's Jean Grey, a member of the original X-Men team, inherit the cosmic Phoenix Force, which results in the hero's corruption, causing her to battle with the X-Men. While this narrative is one of Marvel Comics' strongest moments, the story never managed to translate well to the screen. With mutants becoming more prevalent in the MCU, this is one storyline that Marvel Studios should actively avoid repeating.
Why Marvel Should Avoid The Dark Phoenix Storyline
Taking into that the Dark Phoenix Saga has already been adapted twice over at Fox, it's likely that avid viewers of Marvel films are already familiar with the storyline and don't need to see it played out again. Marvel Studios have taken this approach already with the Spider-Man: Homecoming making the conscious decision to focus on a later point in his career instead of repeating something which had been adapted twice already in 2002 and 2012. There's no doubt that if Marvel Studios did decide to adapt the Dark Phoenix Saga for the MCU, they'd fare infinitely better than the attempts at Fox, but the story will get old very quickly, and there are plenty of other strong X-Men storylines that could be adapted in its place.
On top of this, many of the plot points from the Dark Phoenix Saga have already been recycled into other MCU projects, most prominently in Marvel Studios' first Disney+ series, WandaVision, which rules out an MCU Dark Phoenix story due to their striking and surprising similarities. Since many of the key plot points have already been used in various MCU projects, it would be completely unnecessary and slightly jarring to reuse these moments again just with a new roster of heroes. The X-Men have a rich history in Marvel Comics, with hundreds of story arcs ready to be adapted to film - there's no need for Marvel to tackle the Dark Phoenix Saga once again.
