So I looked up Illuminati on Comic Vine:
Members and Representing
Each member of the Illuminati represents a different aspect of society and point of view, which is part of the reason they formed. Each member is also considered to be an unparalleled master of their domain or area of expertise.
Iron Man (Tony Stark): The master of technology and a founding member of the Avengers. Represents the technological and military/industrial communities. Also represents the Avengers and the type of hero who would work with the government.
Namor: The master of the oceans. Represents the underwater realms and
Atlantis. Also represents the anti-hero.
Mr. Fantastic (Reed Richards): The world's greatest scientific intellect and the leader of the Fantastic Four. Represents the scientific and intellectual community.
Professor X (Charles Xavier): The world's most powerful mutant mind and the founder of the X-Men. Currently deceased, he represented the mutant population and community.
Black Bolt (Blackagar Boltagon): King of the Inhumans. Represented the Inhuman population and community. Also represented royalty. After Black Bolt's death, his widowed wife
Medusa, Queen of the Inhumans, took his place in the Illuminati.
Doctor Strange (Stephen Strange): The master of magic. Represents the mystical/magical community and population, as well as that edge of society.
Captain America (Steve Rogers): The first true super soldier, an unparalleled leader, and master military strategist. Represents the American ideal. After the crisis involving the Hood obtaining a portion of the Infinity Gems, Captain America was invited to join the Illuminati. He agreed after realizing that some things were meant to be kept secret.
Beast (Hank McCoy): Current representative of the mutant population and community after the death of Charles Xavier in
Avengers vs X-Men.
Alternate Realities
On Earth-23099;
Captain Mar-Vell,
Shuri and
Magneto were also members of The Illuminati and were the last heroes to stand against The Black Priests, a group of immensely powerful cosmic beings who have been creating incursions across the Multiverse.
I think logically if we got 6 chairs (or 7 if Prof X has a hover chair) it makes sense that:
Prof Xavier confirmed
Black Panther Shuri or Killmonger (Shuri is smarter, I would go with her. Wakanda has a large army and replaces Namor, who sounds like will be introduced in BP2)
Captain Marvel or Captain Photon aka Monica Rambeau replaces Black Bolt
Reed Richards (either Krasinski or Gruffold)
Captain Carter (shield teased in the poster)
Iron Cruise (cause you have to deliver on that)
Mordo replaces Strange
Any roster would be disappointing to me if we are missing a Reed Richards and/or an Iron Man.