2019's Avengers 4 will serve as the culmination of a years-long story arc, and if Avengers: Infinity War is any indication, it could lead some of our heroes to sacrifice themselves for the greater good. In an emotional thank you, Chris Evans (who plays Steve Rogers aka Captain America) seemed to indicate it could be his own character on the chopping block--or at least we're meant to think he is.
Calling it an "emotional day" and noting the amount of time he played the character definitely implies a sense of finality, but that doesn't necessarily mean Cap is a goner. Joe and Anthony Russo, who directed Avengers: Infinity War and the untitled Avengers 4 (scheduled for release in May 2019), have gone to great lengths to protect plot reveals--even going so far as to produce a fake-out version of a scene for the Infinity War trailer that never appeared in the finished film.
Officially wrapped on Avengers 4. It was an emotional day to say the least. Playing this role over the last 8 years has been an honor. To everyone in front of the camera, behind the camera, and in the audience, thank you for the memories! Eternally grateful.— Chris Evans (@ChrisEvans) October 4, 2018
It's possible Evans was recruited by the Russos to set out audience expectations so they can be subverted later. It's also possible, of course, that he is putting the character to bed and sincerely got caught up in the moment. Or all this tea-leaf reading is meaningless because he was just showing appreciation to the crew after a very long shoot.
For the time being, fans are attempting to guess the title of the next movie, which Marvel has kept carefully under wraps. Writer Christopher Markus said the next film will be very different, summarizing it as: "We broke your heart. Now we're going to blow your mind."
As for Evans himself, his next project has been revealed, and it will see him team up with James Bond actor Daniel Craig and Star Wars: The Last Jedi director Rian Johnson.