As fans analyze every line in Avengers: Endgame, people noticed Okoye mentioning an earthquake in the ocean. Obviously since it’s connected to the ocean, fans think that was hinting at Namor. When the Russos were on MTV’s Happy, Sad, Confused podcast they asked them and Joe Russo didn’t give a straight answer, just giving a sly “Maaaaybe” about the Namor question. That could be an intentional misdirection (as the Russos tend to do) to keep people off the scent, as Atlantis isn’t the only undersea city in the Marvel universe and those who live in the other undersea city have a movie going into production this year.
Namor is from Atlantis, but there’s another ancient lost city of legend that appears in Marvel Comics. Under the ruins of Lemuria the Deviants (of The Eternals) have an advanced undersea city:
Outside of the hopes and dreams of fans, there has actually been nothing official saying Namor is coming to the MCU yet and the character has a complicated rights history similar to Hulk.
On the other hand, The Eternals is in the process of filling out its large cast, will begin filming later this summer, and will likely release in theaters next year. It could make a lot of sense for Avengers: Endgame to put in an Easter Egg for the movies coming next year. There was one for Black Widow (how she didn’t know her father’s name, but Red Skull did), so one for Eternals in the form of an undersea earthquake at their city would make a lot of sense…