This one feels somewhat unlikely, if only because Jolie has a long history of playing overtly tough characters, so giving her a name like Pixie would seem like a weird choice for a casting director to make -- especially if it was the first piece of casting for the whole movie. Still, here's the rundown: Pixie is a member of the First Line, who uses her powers to turn people to stone while disguising it as an effect of her "pixie dust."
This is a solid candidate if they hew close to the comics, if only because she is a largely blank slate who died in battle ages ago. One of the original Eternals, this could theoretically be a way to get an actor like Jolie if she does not want to be locked down to a multi-picture deal, by setting her up for a heroic sacrifice at some point in the film.
In the comics, Shastra has only figured into three issues -- and they were all
What If...? comics. She had a fourth appearance, but it was in the old Marvel Handbook, and basically just gave a summary of what little was known about her up to then and presumably confirmed that outside of the world of
What If...?, she is still a character who existed in the Marvel Universe.
This is another solid candidate, in part because of her very explicit ties to Thanos and the potential to give her a story that would feel at home in the MCU. In the comics, Sui-San is a descendant of Uranos's followers on Titan, and the only survivor of the war on the surface of Titan. She was found by A'lars, who with her, founded the new Eternals of Titan -- something that certainly sounds like the makings of an origin movie to me. Sui-San's children included Eros and Thanos -- the latter of whom killed her during his attack on Titan, when he dissected her with a medical kit in the hopes of learning why he was different from other children.
It has been said that
Avengers: Infinity War was really a movie about Thanos. Well, if you want a prequel to a movie like that, it seems like the life and death of his mother (whom he killed in what could arguably be called the moment he became truly irredeemable) is a solid place to start.
These artificial structures that present as Eternals could be an interesting use of Jolie, essentially shunting her into a role not dissimilar to the one filled by Annette Bening in
Captain Marvel.
Because the Uni-Mind -- a gestalt entity created by "collective energy of participants in the Ritual of the Uni-Mind" -- has long been a part of the Eternals mythology, similar entities have cropped up in various groups attached to the concept. Per the description on Wikipedia, "Eternals, Humans, Deviants and Brethren have been a part of Uni-Minds."
Zuras was the first Eternal to form a Uni-Mind, used it to determine who should become Prime Eternal -- and since then, the Prime Eternal alone has the power initiate a Uni-Mind. Following Zuras' death, a Uni-Mind left Earth, containing most of the Eternals' population. The Uni-Mind apparently still exists, though Ajak, and possibly others, have left it behind.
The Overmind, similarly, is the collected mind of the Eternals of Eyung. This one, strangely, has a kind of arch-nemesis: The former Eternals of Gigantus who were the mortal enemies of the Eternals of Eyung. All the Eternals of Gigantus are now deceased. They had placed their minds into a gestalt being much in the same way the Eternals from Eyung did with the Overmind. This creature was accidentally killed by The Stranger, who later claimed to be the composite Gigantian Eternal during an encounter with the Overmind.
https://comicbook.com/marvel/2019/03/28/who-is-angelina-jolie-playing-in-marvels-the-eternals-/#7