Phase 4 is kicking off a whole new era of the Marvel Cinematic Universe, and there are going to be a lot of new characters introduced to audiences. It’s been long rumored that we’d see Namor pop up in the MCU, and many believe it’ll be in Black Panther II, but if you’ve watched the Infinity Saga; you’ll know how Marvel likes to set things up far in advance.
The Super Soldier Serum was introduced in The Incredible Hulk before we saw Captain America: The First Avenger. That movie then introduced the concept of Vibranium, before Wakanda was named in Avengers: Age of Ultron (before that it was seen on a map in Iron Man 2).
Much like the early references to Wakanda, a new rumor says we’ll get a nod to Namor in Eternals. The rumor says that at some point in the movie (possibly a montage or something) we’ll see the sinking of Atlantis on screen.
Eternals is set over 35,000 years in the MCU, and we already know that we’ll be seeing ancient Babylon in the movie. If we’re going that far back in the past of the MCU, it’s the perfect opportunity for them to show something like Atlantis sinking, which would of course be a big setup to introducing Namor for a bigger role in the future.