I could see the Celestials playing into the plot as the reason why they don't step in until the Thanos snap. Anytime they interfere even a little, the Celestial punishes them. And then the movie ends with them expelling the Earth Celestial (which then attracts other big bad like maybe a certain world eater).
And I (shouldn't) *hope* that Thanos ties into the Eternals with out much of a retcon.