Did Avengers: Endgame Tease Namor?
1. What We Know Of The Rights Situation So Far
Of course, those familiar with Namor over the last decade will also likely be aware of the snafu revolving around the character's on screen rights. At first they were with Universal, then Marvel, but then not with Marvel, and then somehow with Marvel again. Point being, the whole situation is a tad convoluted and it's only recently that the House of Ideas has publicly declared the character's availability.
Although Marvel Studios head honcho Kevin Feige said that Namor was "definitively" at Universal back in 2013, chatter in the years since has indicated pretty much the exact opposite. Feige again weighed into the topic of Namor in 2018 while talking to IGN, stating that "there’s a way to probably figure it out but it does have... it’s not as a clean or clear as the majority of the other characters."
It seems as though whatever Marvel had to work out with those producers still attached to the Namor license has been worked out, but we're still waiting on a definitive answer.
Doctor Strange director Scott Derrickson mysteriously deleted a tweet referencing Namor earlier in the year, and if the Sub-Mariner's situation is even vaguely similar to the Hulk's, it could be that Marvel are able to feature the character in other MCU films, but without the prospect of a solo feature to come.