Prolly too soon for speculation, but I'm thinking we're going to see a version of Eternity soon.
He was alluded to by name in GotG vol2, the Mind Stone has been shown to be a sort of separate consciousness from Vision, the Soul Stone's entire trial shows there's a kind of morality and desire to punish hubris, so I feel they're also going to adapt the Stones' origin as a single 'original being' but combine it with the concept of Eternity.
Dormammu's depiction in Dr Strange is also actually fairly similar to Eternity, so they may set this concept that each 'universe' can have its own all-encompassing entity.
Maybe not a full manifestation, but since Adarm Warlock is also going to be a thing, maybe Eternity operating through an avatar like Adam? To confront Thanos similar to the comics?