There are major and minor spoilers ahead for Avengers: Endgame, so proceed at your own risk.
Did you ever think that Avengers: Endgame would end up being a sequel to Captain America: The First Avenger? The 22nd film in the Marvel Cinematic Universe ends with something that was promised way back in the fifth installment. After endless flirting throughout the movie, Steve Rogers (Chris Evans) and Peggy Carter (Hayley Atwell) finally decide to go out on a date and have a "first dance." The only problem? Steve is about to crash into icy waters, presumably killing himself, in order to destroy the weapons on the plane he's piloting. Peggy, near hysterics, begs him not to, but this is Captain America we're talking about. Of course, he's going to risk his life for others.
So in a surprising twist, Avengers: Endgame ends with Steve and Peggy finally having the dance that was first promised in the 1940s. It's not a dream sequence, and it's not even a flashback. For both Steve and Peggy, it's real-life, because Steve has gone back in time to stay with Peggy and live out his time in the past. (This is possible because Endgame includes a whole lot of time travel, and after seeing Peggy in the 1970s, Steve realizes that she's still the only girl for him. While returning the Infinity Stones to their rightful place in time, Steve ops not to return to the present day, leaving him and Peggy to then live happily ever after.)
And while it's an incredibly touching scene and, clearly, one that we've been building to for years, it also manages to dash any hope we had for a revival of ABC's Agent Carter. Sure, Steve has his happy ending, but Agent Carter viewers do not have one whatsoever.
Agent Carter, which lasted for two seasons and a mere 18 episodes between 2015-2016, told the story of Peggy's rise through the S.H.I.E.L.D. ranks while dealing with the aftermath of Steve's death. Peggy went on to become a founding member of S.H.I.E.L.D., and Atwell has appeared as the character a handful of other times through the MCU (including even Agents of S.H.I.E.L.D.). As Peggy tells Steve in Captain America: The Winter Soldier, she's lived a full life without him and went onto have a husband and kids; Peggy then dies during Captain America: Civil War and Steve is one of the pallbearers at her funeral.
Atwell has been a presence in the MCU for the last decade and it was a horrible shame when Agent Carter was canceled since that meant she wouldn't be the focal point of any story anymore. While certainly a supporting character, she was a fan favorite (and one of the first female heroes to join the MCU). After Agent Carter's cancelation, there was a push to get it picked up somewhere else — namely on Netflix, which was already starting to build its slate of Marvel television. But those talks fell through, and Agent Carter was never revived for a third season.
Then, of course, Disney+ came along. Currently, the Disney streaming service has five shows in development that focus on Marvel characters who haven't received their own stand-alone movie. As conversations around these shows started picking up, there was, of course, a hope that Agent Carter might make its way there, too (along with, you know, all the Marvel shows Netflix canceled). It seemed highly likely. Maybe not at the launch of Disney+, but somewhere down the line.
And then Steve had to go back in time and stay with Peggy, essentially rewiring her story from the end of The First Avenger and onward.
Agent Carter is supposed to take place roughly four years after the events of The First Avenger, but it's unclear when Steve actually joins Peggy in the past. Is it immediately after First Avenger? During the second season of Agent Carter (which brought Peggy to Los Angeles, even though in the 1970s she's working in New Jersey, but that's neither here nor there). Who knows? But he's there, and just speaking in the frankest of terms, Chris Evans is not joining Hayley Atwell for any hypothetical series on Disney+.
While the rules of time travel are a little bit murky in Endgame, it's also possible that now there are two different timelines: one where Steve and Peggy are together, and one where they're not. Sure, eventually we could have another Agent Carter series focusing on the latter, pretending Endgame never happened, but that's unlikely. Steve and Peggy are together like they were always supposed to be, and no one's going to want to watch their story rewritten again.
It's wonderful that Steve and Peggy finally got their dance, it's just a shame it happened at the expense of continuing Peggy Carter's story.
Starring Evans, Atwell, Robert Downey Jr., Chris Hemsworth, Mark Ruffalo, Jeremy Renner, Paul Rudd, Karen Gillan, Scarlett Johansson, Gwyneth Paltrow, Josh Brolin, and Bradley Cooper as the voice of Rocket Racoon, Avengers: Endgame is out in theaters now.