The X-men's MCU intro should act as if we know but tell us who they are anyway (especially since we may have a new casts portraying our beloved X-men).
As far as the regular villains, I'd like to see the MCU have:
-Magneto be a threat that has retired via Avalon, Asteroid M or Genosha... basically having a sovereign nation of mutants he lives amongst outside human society
-I would like to see the Brotherhood reintroduced as a new terrorist threat led by Mystique in secret who operates more as Raven Darkholme, secretary of defense for the government. Destiny acts as a defacto leader of the Brotherhood (Pyro, Blob, Avalanche, Toad & Phantasia).
-Trask & the Sentinels would be a new program to police the growing mutant threat... but of course the Sentinels ultimately turn against humanity
For their debut, I had the idea of going the "Pryde of the X-men" route and introduce us to the team via a new student, like Cipher (Young X-men). I remember reading she told Cyclops she was hiding at the school from someone in the comics. I thought what if, in the cinematic version, she is the daughter of Moses Magnum? An eco-terrorist, Cipher pulls the X-men into his plot to rise to power. I just read he was given his powers by Apoc too, which is a good subplot building to big A coming onto the scene in the MCU...
"I am the way, the truth, and the life: no man cometh unto the Father, but by me."- Jesus
John 14:6
Honestly they should just steal the Inhuman storyline of mutants being a secret society that's forced to go public. They stole enough from the X-Men these past few years, pay em back. Set up a skrull imposter crisis story post Captain Marvel in the marvel day and you've got the perfect way to explain the hatred and fear of these randomly superpowered humanoid race of people popping up.
Depending on when the Fox deal goes through, I wouldn't be surprised if X-Force/DP3 ends up being the "first" official MCU X-Movie. Especially now that they have an open slot in 2020.
Marvel casted Katherine Langford for Avengers 4. In my (very optimistic and fertile) mind, she is going to play Rogue! or Kitty. And the X-Men are slowly being introduced in the MCU. Storm in Black Panther 2 is perfection!
A picture would last longer darling...
She's probably Kate Bishop.
Would be a waste if she wasn't cast as Rogue, but that's a pipe dream I guess. It would make sense though to introduce the X-Men through the Avengers somehow, then the mutants get their own film. Here's to hoping this Langford actress is at odds with Carol Danvers in Avengers 4