He had speculated on that possibility, after a little wink in Avengers: Endgame. But nothing is further from reality: the Russo brothers have assured that, at least for the moment, Namor does not enter into his plans in order to enter the UCM.
Anyway, while we wait to know more details about the plans of MarveIn the face of Phase 4 of the UCM, the rumors are closed. In other words, everything seems to indicate that the endgame aquatic “earthquake” will stay just that: a simple earthquake.
What’s more, that was exactly the way they denied it, according to ComicBook. To be more concrete, Christopher Markus would have put firewood to the fire with the theme, to which the Russo would have answered with a “Some people can interpret it that way, but it could just be an earthquake.”.
If only for those statements, the doors of the ocean they would not be completely closed. The problem comes when Namor is, precisely, one of those characters to whom Marvel does not have such an easy access (for rights issues).
However, that same problem of licensing is something that does not necessarily have to be bad in the case at hand. That is since the Marvel films are getting more success, Kevin Feige is working on recovering more licenses.
And, in a way, that has to be a reason for hope for the most hardcore fans of comics. Meanwhile, we will be expectant before the announcements that Feige himself could have saved for the next Comic-Con of San Diego.