https://www.ign.com/articles/2019/03...-men-character
So this article, and a couple of other articles, have some interesting speculation about where the Captain Marvel sequel could go. The gist of it is that since Mystique and Rogue were originally introduced as Carol Danvers villains in the old Ms. Marvel series, her movie could be the best place to introduce the MCU versions of these characters - and also get a more 'comic-accurate' Rogue, powers-wise, by adapting the story where Rogue steals Carol's powers.
It does make me wonder if this could indeed be the right strategy for slowly introducing X-men characters to the MCU, by seeding them into other films where it makes sense.
So maybe Rogue and Mystique (and other Brotherhood members, possible?) could show up in a Captain Marvel film. The Black Widow film could feature an extended cameo by Wolverine, The Black Panther sequel could introduce Storm.
These characters wouldn't necessarily be introduced as 'mutants' specifically. They would have abilities and be referred to as enhanced individuals, and play their roles in the respective films. All along there might be easter eggs and background references about a 'mutant epidemic' and growing sub-communities of super-powered individuals.
And all of these will ultimately seed into an X-men film where these characters and the subplots teased all come together - much like the Avengers once did.