It's important to note that there are major SPOILERS for Infinity War below, so read ahead at your own risk. The Russo Brothers have accomplished an amazing feat with Infinity War, which is the beginning of the end of the Marvel Cinematic Universe with next year's Avengers 4 ending phase 3. James Gunn has declared that Guardians of the Galaxy Vol. 3 will kick of the next phase of the MCU and Marvel Studios boss Kevin Feige has already stated that The Eternals are one of the many ideas being developed for possible inclusion in phase 4. With that in mind, Infinity War has a nod to The Eternals, which means that these talks have been going on for quite some time.
SPOILERS start now. The location of the Soul Stone has been an MCU mystery for a decade now, which has finally been solved, thanks to Infinity War. In the movie, Gamora leads Thanos to Vormir to retrieve the Soul Stone and save Nebula's life. When they arrive, they climb a mountain and run in to the guardian of the Soul Stone, who just happens to be Red Skull. He's been on Vormir by himself for years, but he knows about Thanos and calls him "Thanos, son of A'lars."
The fact that Red Skull brings up the name of A'lars is a big deal for Marvel fans. A'lars, also known as the Mentor in the comics, is Thanos' father and the founder of the Eternals' colony on Titan. This could be the very early seed planting for The Eternals to show up in the MCU for phase 4. A'lars tries to not acknowledge the actions of his son in the comics and only really does after Thanos kills his mother, Sui-San.
A'lars looks human in the comics because he does not possess the "Deviant Gene" like Thanos and some of the other Eternals. In Infinity War, Thanos uses the Reality Stone to show Doctor Strange what Titan looked like in the past, featuring inhabitants that look human. Thanos' appearance is one of the reasons that he was cast aside, but Infinity War also proves that he was also cast aside because of his philosophies as well. His ideas of genocide to further the universe didn't sit well with the Eternals.
While it's a small mention, it could be the first mention of The Eternals in the MCU, setting up the next phase. Kevin Feige has revealed that the project is being talked about currently, but it may have already been decided, thanks to the little clue from Infinity War. The next phase of the MCU will be more cosmic, focusing on some Marvel characters from all around the universe, which as previously noted, will be set up by Guardians of the Galaxy Vol. 3 as well as the upcoming Captain Marvel. You can read more about The Eternals over at Marvel Studios.