I don't think anyone has posted this yet, but the latest TV promo has confirmed that the group that maybe-Xavier is part of, is the Illuminati.
So that raises the question of who the members of this Illuminati are, could this be how they introduce Reed Richards and Namor, along with maybe-Xavier? After the trainwreck of The Inhumans, I doubt we'll see Black Bolt, unless they decide to give it another try with a multiversal variant of him.
Or maybe it will be all characters from past films, with Patrick Stewart's Xavier, Ioan Gruffud's Reed Richards, Eric Banna's Bruce Banner, and either Toby Maguire or Andrew Garfield's Peter Parker?
The Illuminauti don't have to be MCU characters in this, it could be a multiverse group in this incarnation, so we could get a bunch of weird cameos. I'm hoping for the 2000s FF Movies version of Reed, and I remember people used to think/hope that Vin Diesel would play Black Bolt, which is an idea I don't like if its ongoing appearances but would love as a multiverse cameo thing.