Will The Eternals be featured in Thor: Ragnarok? We already saw a glimpse of their creators, The Celestials in Guardians of the Galaxy, so it's not completely outside the realm or possibility.
During Ragnarok's sizzle reel last night, multiple fans in attendance are reporting that they saw what they believe to be The Eternals cut among the footage. There was reportedly a throne room scene with multiple deity-looking figures with armor very reminiscenof the designs Jack Kirby first created for the race of superhumans resultant from prehistoric experiments by The Celestials on early human life. Perhaps it will be explained in Thor: Ragnarok that The Celestials left the Infinity Stones on Earth long ago for safe keeping and while there, created The Eternals to guard them? Of course, it would need to be explained why The Eternals have been absent in the MCU until now. With Hela, Surtur, Fenrir, Loki sitting upon the Asgardian throne and elements of Planet Hulk - could Thor: Ragnarok finally be the Thor film we've all been waiting for?
Of course, consider this a rumor until we recieve confirmation from Marvel Studios but in the meantime, start developing those theories on how The Eternals could factor into Thor: Ragnarok and the larger MCU.